diff --git a/src/command_type.h b/src/command_type.h
index dae768104b..8f3cbedd93 100644
--- a/src/command_type.h
+++ b/src/command_type.h
@@ -294,6 +294,7 @@ enum Commands : uint16_t {
 
 	CMD_CREATE_SUBSIDY,               ///< create a new subsidy
 	CMD_COMPANY_CTRL,                 ///< used in multiplayer to create a new companies etc.
+	CMD_COMPANY_ADD_ALLOW_LIST, ///< Used in multiplayer to add a client's public key to the company's allow list.
 	CMD_CUSTOM_NEWS_ITEM,             ///< create a custom news message
 	CMD_CREATE_GOAL,                  ///< create a new goal
 	CMD_REMOVE_GOAL,                  ///< remove a goal
diff --git a/src/company_base.h b/src/company_base.h
index 9d4a3dc87b..d6ab4a8fd1 100644
--- a/src/company_base.h
+++ b/src/company_base.h
@@ -75,6 +75,8 @@ struct CompanyProperties {
 	uint32_t president_name_2;         ///< Parameter of #president_name_1
 	std::string president_name;      ///< Name of the president if the user changed it.
 
+	NetworkAuthorizedKeys allow_list; ///< Public keys of clients that are allowed to join this company.
+
 	CompanyManagerFace face;         ///< Face description of the president.
 
 	Money money;                     ///< Money owned by the company.
diff --git a/src/company_cmd.cpp b/src/company_cmd.cpp
index 6fa44f4bc5..d937479419 100644
--- a/src/company_cmd.cpp
+++ b/src/company_cmd.cpp
@@ -980,6 +980,24 @@ CommandCost CmdCompanyCtrl(DoCommandFlag flags, CompanyCtrlAction cca, CompanyID
 	return CommandCost();
 }
 
+/**
+ * Add the given public key to the allow list of this company.
+ * @param flags Operation to perform.
+ * @param public_key The public key of the client to add.
+ * @return The cost of this operation or an error.
+ */
+CommandCost CmdCompanyAddAllowList(DoCommandFlag flags, const std::string &public_key)
+{
+	if (flags & DC_EXEC) {
+		if (Company::Get(_current_company)->allow_list.Add(public_key)) {
+			InvalidateWindowData(WC_CLIENT_LIST, 0);
+			SetWindowDirty(WC_COMPANY, _current_company);
+		}
+	}
+
+	return CommandCost();
+}
+
 /**
  * Change the company manager's face.
  * @param flags operation to perform
diff --git a/src/company_cmd.h b/src/company_cmd.h
index 8493549c58..5f818c4b8f 100644
--- a/src/company_cmd.h
+++ b/src/company_cmd.h
@@ -18,6 +18,7 @@ enum ClientID : uint32_t;
 enum Colours : uint8_t;
 
 CommandCost CmdCompanyCtrl(DoCommandFlag flags, CompanyCtrlAction cca, CompanyID company_id, CompanyRemoveReason reason, ClientID client_id);
+CommandCost CmdCompanyAddAllowList(DoCommandFlag flags, const std::string &public_key);
 CommandCost CmdGiveMoney(DoCommandFlag flags, Money money, CompanyID dest_company);
 CommandCost CmdRenameCompany(DoCommandFlag flags, const std::string &text);
 CommandCost CmdRenamePresident(DoCommandFlag flags, const std::string &text);
@@ -25,6 +26,7 @@ CommandCost CmdSetCompanyManagerFace(DoCommandFlag flags, CompanyManagerFace cmf
 CommandCost CmdSetCompanyColour(DoCommandFlag flags, LiveryScheme scheme, bool primary, Colours colour);
 
 DEF_CMD_TRAIT(CMD_COMPANY_CTRL,             CmdCompanyCtrl,           CMD_SPECTATOR | CMD_CLIENT_ID | CMD_NO_EST, CMDT_SERVER_SETTING)
+DEF_CMD_TRAIT(CMD_COMPANY_ADD_ALLOW_LIST,   CmdCompanyAddAllowList,   CMD_NO_EST,                                 CMDT_SERVER_SETTING)
 DEF_CMD_TRAIT(CMD_GIVE_MONEY,               CmdGiveMoney,             0,                                          CMDT_MONEY_MANAGEMENT)
 DEF_CMD_TRAIT(CMD_RENAME_COMPANY,           CmdRenameCompany,         0,                                          CMDT_OTHER_MANAGEMENT)
 DEF_CMD_TRAIT(CMD_RENAME_PRESIDENT,         CmdRenamePresident,       0,                                          CMDT_OTHER_MANAGEMENT)
diff --git a/src/network/core/config.h b/src/network/core/config.h
index e74cfb2fff..99e6a3bd94 100644
--- a/src/network/core/config.h
+++ b/src/network/core/config.h
@@ -96,5 +96,10 @@ static const uint NETWORK_MAX_GRF_COUNT             =   255;
  * This is related to \c X25519_KEY_SIZE in the network crypto internals.
  */
 static const uint NETWORK_SECRET_KEY_LENGTH = 32 * 2 + 1;
+/**
+ * The maximum length of the hexadecimal encoded public keys, in bytes including '\0'.
+ * This is related to \c X25519_KEY_SIZE in the network crypto internals.
+ */
+static const uint NETWORK_PUBLIC_KEY_LENGTH = 32 * 2 + 1;
 
 #endif /* NETWORK_CORE_CONFIG_H */
diff --git a/src/network/core/tcp_game.h b/src/network/core/tcp_game.h
index ce6f9bdcea..d29a17d8e0 100644
--- a/src/network/core/tcp_game.h
+++ b/src/network/core/tcp_game.h
@@ -202,7 +202,8 @@ protected:
 	 * Send information about a client:
 	 * uint32_t  ID of the client (always unique on a server. 1 = server, 0 is invalid).
 	 * uint8_t   ID of the company the client is playing as (255 for spectators).
-	 * string  Name of the client.
+	 * string Name of the client.
+	 * string Public key of the client.
 	 * @param p The packet that was just received.
 	 */
 	virtual NetworkRecvStatus Receive_SERVER_CLIENT_INFO(Packet &p);
diff --git a/src/network/network.cpp b/src/network/network.cpp
index b37b1aaf68..5e16ae49fb 100644
--- a/src/network/network.cpp
+++ b/src/network/network.cpp
@@ -165,10 +165,12 @@ bool NetworkAuthorizedKeys::Contains(std::string_view key) const
 /**
  * Add the given key to the authorized keys, when it is not already contained.
  * @param key The key to add.
- * @return \c true when the key was added, \c false when the key already existed.
+ * @return \c true when the key was added, \c false when the key already existed or the key was empty.
  */
 bool NetworkAuthorizedKeys::Add(std::string_view key)
 {
+	if (key.empty()) return false;
+
 	auto iter = FindKey(this, key);
 	if (iter != this->end()) return false;
 
diff --git a/src/network/network_base.h b/src/network/network_base.h
index 0b717163f7..0b3cbde7d2 100644
--- a/src/network/network_base.h
+++ b/src/network/network_base.h
@@ -24,6 +24,7 @@ extern NetworkClientInfoPool _networkclientinfo_pool;
 struct NetworkClientInfo : NetworkClientInfoPool::PoolItem<&_networkclientinfo_pool> {
 	ClientID client_id;      ///< Client identifier (same as ClientState->client_id)
 	std::string client_name; ///< Name of the client
+	std::string public_key; ///< The public key of the client.
 	CompanyID client_playas; ///< As which company is this client playing (CompanyID)
 	TimerGameEconomy::Date join_date; ///< Gamedate the client has joined
 
diff --git a/src/network/network_client.cpp b/src/network/network_client.cpp
index f6302a40e3..1e6dda3b57 100644
--- a/src/network/network_client.cpp
+++ b/src/network/network_client.cpp
@@ -608,6 +608,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::Receive_SERVER_CLIENT_INFO(Pac
 	Debug(net, 9, "Client::Receive_SERVER_CLIENT_INFO(): client_id={}, playas={}", client_id, playas);
 
 	std::string name = p.Recv_string(NETWORK_NAME_LENGTH);
+	std::string public_key = p.Recv_string(NETWORK_PUBLIC_KEY_LENGTH);
 
 	if (this->status < STATUS_AUTHORIZED) return NETWORK_RECV_STATUS_MALFORMED_PACKET;
 	if (this->HasClientQuit()) return NETWORK_RECV_STATUS_CLIENT_QUIT;
@@ -632,6 +633,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::Receive_SERVER_CLIENT_INFO(Pac
 
 		ci->client_playas = playas;
 		ci->client_name = name;
+		ci->public_key = public_key;
 
 		InvalidateWindowData(WC_CLIENT_LIST, 0);
 
@@ -651,6 +653,7 @@ NetworkRecvStatus ClientNetworkGameSocketHandler::Receive_SERVER_CLIENT_INFO(Pac
 	if (client_id == _network_own_client_id) this->SetInfo(ci);
 
 	ci->client_name = name;
+	ci->public_key = public_key;
 
 	InvalidateWindowData(WC_CLIENT_LIST, 0);
 
diff --git a/src/network/network_server.cpp b/src/network/network_server.cpp
index 8bd2f4c7e4..c1bfdde98c 100644
--- a/src/network/network_server.cpp
+++ b/src/network/network_server.cpp
@@ -332,6 +332,7 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::SendClientInfo(NetworkClientIn
 		p->Send_uint32(ci->client_id);
 		p->Send_uint8 (ci->client_playas);
 		p->Send_string(ci->client_name);
+		p->Send_string(ci->public_key);
 
 		this->SendPacket(std::move(p));
 	}
@@ -959,6 +960,7 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::Receive_CLIENT_IDENTIFY(Packet
 	ci->join_date = TimerGameEconomy::date;
 	ci->client_name = client_name;
 	ci->client_playas = playas;
+	ci->public_key = this->peer_public_key;
 	Debug(desync, 1, "client: {:08x}; {:02x}; {:02x}; {:02x}", TimerGameEconomy::date, TimerGameEconomy::date_fract, (int)ci->client_playas, (int)ci->index);
 
 	/* Make sure companies to which people try to join are not autocleaned */
@@ -1177,6 +1179,23 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::Receive_CLIENT_COMMAND(Packet
 		}
 	}
 
+	if (cp.cmd == CMD_COMPANY_ADD_ALLOW_LIST) {
+		/* Maybe the client just got moved before allowing? */
+		if (ci->client_id != CLIENT_ID_SERVER && ci->client_playas != cp.company) return NETWORK_RECV_STATUS_OKAY;
+
+		std::string public_key = std::get<0>(EndianBufferReader::ToValue<CommandTraits<CMD_COMPANY_ADD_ALLOW_LIST>::Args>(cp.data));
+		bool found = false;
+		for (const NetworkClientInfo *info : NetworkClientInfo::Iterate()) {
+			if (info->public_key == public_key) {
+				found = true;
+				break;
+			}
+		}
+
+		/* Maybe the client just left? */
+		if (!found) return NETWORK_RECV_STATUS_OKAY;
+	}
+
 	if (GetCommandFlags(cp.cmd) & CMD_CLIENT_ID) NetworkReplaceCommandClientId(cp, this->client_id);
 
 	this->incoming_queue.push_back(cp);
@@ -1541,7 +1560,7 @@ NetworkRecvStatus ServerNetworkGameSocketHandler::Receive_CLIENT_MOVE(Packet &p)
 	if (company_id != COMPANY_SPECTATOR && !Company::IsValidHumanID(company_id)) return NETWORK_RECV_STATUS_OKAY;
 
 	/* Check if we require a password for this company */
-	if (company_id != COMPANY_SPECTATOR && !_network_company_states[company_id].password.empty()) {
+	if (company_id != COMPANY_SPECTATOR && !Company::Get(company_id)->allow_list.Contains(this->peer_public_key) && !_network_company_states[company_id].password.empty()) {
 		/* we need a password from the client - should be in this packet */
 		std::string password = p.Recv_string(NETWORK_PASSWORD_LENGTH);
 
@@ -2275,13 +2294,9 @@ void NetworkServerNewCompany(const Company *c, NetworkClientInfo *ci)
 		/* ci is nullptr when replaying, or for AIs. In neither case there is a client. */
 		ci->client_playas = c->index;
 		NetworkUpdateClientInfo(ci->client_id);
+		Command<CMD_COMPANY_ADD_ALLOW_LIST>::SendNet(STR_NULL, c->index, ci->public_key);
 		Command<CMD_RENAME_PRESIDENT>::SendNet(STR_NULL, c->index, ci->client_name);
-	}
 
-	if (ci != nullptr) {
-		/* ci is nullptr when replaying, or for AIs. In neither case there is a client.
-		   We need to send Admin port update here so that they first know about the new company
-		   and then learn about a possibly joining client (see FS#6025) */
 		NetworkServerSendChat(NETWORK_ACTION_COMPANY_NEW, DESTTYPE_BROADCAST, 0, "", ci->client_id, c->index + 1);
 	}
 }
diff --git a/src/saveload/company_sl.cpp b/src/saveload/company_sl.cpp
index 50a247da54..651daa1bcb 100644
--- a/src/saveload/company_sl.cpp
+++ b/src/saveload/company_sl.cpp
@@ -450,6 +450,8 @@ static const SaveLoad _company_desc[] = {
 	    SLE_VAR(CompanyProperties, president_name_2, SLE_UINT32),
 	SLE_CONDSSTR(CompanyProperties, president_name,  SLE_STR | SLF_ALLOW_CONTROL, SLV_84, SL_MAX_VERSION),
 
+	SLE_CONDVECTOR(CompanyProperties, allow_list, SLE_STR, SLV_COMPANY_ALLOW_LIST, SL_MAX_VERSION),
+
 	    SLE_VAR(CompanyProperties, face,            SLE_UINT32),
 
 	/* money was changed to a 64 bit field in savegame version 1. */
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index db9de245c9..94c1303acc 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -379,6 +379,8 @@ enum SaveLoadVersion : uint16_t {
 	SLV_SCRIPT_RANDOMIZER,                  ///< 333  PR#12063 v14.0-RC1 Save script randomizers.
 	SLV_VEHICLE_ECONOMY_AGE,                ///< 334  PR#12141 v14.0 Add vehicle age in economy year, for profit stats minimum age
 
+	SLV_COMPANY_ALLOW_LIST,                 ///< 335  PR#12337 Saving of list of client keys that are allowed to join this company.
+
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };
 
diff --git a/src/tests/test_network_crypto.cpp b/src/tests/test_network_crypto.cpp
index 2c8734e11b..1cba244c9b 100644
--- a/src/tests/test_network_crypto.cpp
+++ b/src/tests/test_network_crypto.cpp
@@ -18,6 +18,7 @@
 
 /* The length of the hexadecimal representation of a X25519 key must fit in the key length. */
 static_assert(NETWORK_SECRET_KEY_LENGTH >= X25519_KEY_SIZE * 2 + 1);
+static_assert(NETWORK_PUBLIC_KEY_LENGTH >= X25519_KEY_SIZE * 2 + 1);
 
 class MockNetworkSocketHandler : public NetworkSocketHandler {
 public: