Republican lawmakers in Tennessee are threatening to withhold tax incentives for a potential expansion of Volkswagen’s automotive plant there if auto workers decide to join the United Auto Workers.

Fifteen hundred workers will vote Wednesday through Friday on whether to join the UAW, according to the Detroit Free Press.

But Americans for Tax Reform President Grover Norquist and other lawmakers are trying to steer the auto workers from joining the union.

“It has been widely reported that Volkswagen has promoted a campaign that has been unfair, unbalanced and, quite frankly, un-American in the traditions of American labor campaigns,” Tennessee State Sen. Bo Watson said in a statement according to the Free Press. “Should the workers choose to be represented by the United Auto Workers, then I believe additional incentives for expansion will have a very tough time passing the Tennessee Senate.”

The state’s governor, Bill Haslam (R), through a spokesman, signaled that tax incentives would likely be part of any discussion with Volkswagen auto workers going forward.

“Any discussions of incentives are part of additional and continued talks with VW, which we look forward to,” Haslam spokesman David Smith said.

Norquist and the Center for Worker Freedom have reportedly rented roughly 12 billboards in the Chattanooga area to urge the auto workers not to join the UAW.