As a member of multiple groups in the Commons, you may want to post something (like a call for papers) in multiple group discussions. If you simply copy and paste a post, however, it will be rejected in the second group. This is to prevent spam rather than to keep you from cross-posting. If the text of your posts is at all different, however, you’ll be fine. A good way to do this is to personalize a post for the forum in which it will appear by adding a line at the top, like “Dear members of Twentieth-Century French Literature, I thought you might be interested in this.”
You also have the option to post the same message to multiple groups. Create a new topic in one group and below the editor, above the Submit button, you’ll find a list of your other Commons groups. Select the groups where you’d like the message to be posted. When you publish the post in the original group, it will simultaneously be posted to the other groups you select.