In his speech on Thursday, Brown said: “You look back in history, and some of the worst governments we have ever had, you know, what was one of the first things they do?

“They went after the trade unions. Hitler didn't want unions, Stalin didn't want unions, Mubarak didn't want independent unions. These autocrats in history don’t want independent unions.”

Brown was speaking in the context of the massive rallies union workers have held around the country recently against state governments’ attempts to break collective bargaining rights. But Brown said he was not comparing American workers to workers under those regimes.

“I am not comparing what's happening to the workers in Madison or Columbus to Hitler and Stalin,” said Brown. “But I am saying that history teaches us that unions are a very positive force in society.”