Phillip Hofmeister is president of Michigan Open Carry and was an alternate delegate to the convention from Ingham County at last weekend's convention at the Lansing Center.
Hofmeister said he stepped out of the meeting to see a friend who was taking a smoke break, and the guard stopped him from re-entering the convention while armed.
Hofmeister said he was acting lawfully and the Republican party chose not to let him in.
Republican spokesman Matt Frendewey said the party has to respect rules of the venue. He said the GOP supports the Second Amendment's protections of gun possession.