After creating a union, you will be prompted to invite your friends and previous allies. Check the boxes next to the players you want to see as members of your union and press the Invite button.
You can invite friends and monitor the status of players you’ve already invited in a special window. Just open the settings menu and press the Invitations button.
In the window that opens, you can see the number of active invitations that have been sent out. There can be a maximum of 10.
If you’ve already sent out the maximum number of invitations, but want an additional person in your union, you must cancel one of the other invitations first by pressing the X button. Then press the Invite button and find the name of the player you want to invite.