"We fear that the Republicans are on the march, and that's why we're doing everything we can to stop them," Gerald McEntee, president of the American Federation of State, County and Municipal Employees, told The New York Times. AFSCME is spent $91 million in the two-year campaign cycle, and unions overall have shelled out more than $200 million.
"Republicans are likely to pursue a version of what Samuel Gompers often said: 'Reward your friends and punish your enemies,'" said Joseph McCartin, a labor historian at Georgetown University.
One bill likely to come from a Republican majority would bar employers from ever agreeing to unionization through card check, a common procedure in which an employer recognizes a union as soon as a majority of workers sign pro-union cards, without holding a secret-ballot election.
Another looming proposal would severely limit labor's campaign spending by prohibiting unions from using a member's dues for political purposes without express written permission.
A Republican-led House or Senate also is expected to back free trade agreements that unions oppose.
Swim Week Miami Beach 2014 [PHOTOS]