AP

Patriots receiver Wes Welker is not happy about a $10,000 fine he received for something he says he has no idea was against NFL rules: Wearing a hat without permission.

An NFL spokesman confirmed to the Boston Globe that Welker’s $10,000 fine came for wearing an “unauthorized hat during his postgame interview.”

On Twitter, Welker wrote that he’s been wearing a hat promoting Bonk Breaker energy bars, a company he invests in, all season long, and no one ever told him there was anything wrong with that.

“Got fined by the NFL for wearing a @Bonk_Breaker hat in an interview after the game,” Welker wrote. “Thanks for warning me the other 16 weeks I wore the hat.”

At least Welker found out about the rule during the regular season. As Brian Urlacher found out the hard way, fines for unauthorized hats jump to $100,000 at the Super Bowl.