Union density in the United States has ebbed and flow over the past century. What hasn’t changed is employers’ opposition to trade unions.

Well before the anti-union campaigns of the post-New Deal era, or the right-wing offensives of more recent vintage, employers built networks, developed alliances, and created strategies to stem labor’s rise. Together, employers helped shape a legal, social, and political environment that systematically stacks the deck against workers.

Here are five ways capitalists have tried to fend off unions — often with great success.