CHATTANOOGA (AP) — The United Auto Workers has issued subpoenas to U.S. Sen. Bob Corker, Gov. Bill Haslam and 18 other officials as part of a challenge of a vote rejecting union representation at the Volkswagen plant in Chattanooga.

The subpoenas, dated Wednesday, demand written communications and other documents concerning the union in the weeks preceding the three-day vote at the plant in February. The UAW lost that election 712-626.

The union alleges that Republican politicians interfered with a fair outcome by stating that a UAW win could imperil state incentives for future expansion of Volkswagen's lone U.S. plant.

The union is challenging the result to the National Labor Relations Board. A hearing is scheduled for April 21.

UAW President Bob King said in an emailed statement that the purpose of the investigation "is to determine the truth concerning the third party interference in the February election at Volkswagen's Chattanooga plant."

"The NLRB's rules call for the use of subpoenas as part of this truth-seeking exercise," he said, using the acronym for the labor board. "The UAW hopes that all parties who receive subpoenas will fully comply by providing the NLRB with the requested documents and with their testimony."

Corker's chief of staff, Todd Womack, said in an email that the senator's office has referred the matter to its legal counsel.

"After a stinging defeat, rather than respect the workers' decision the UAW is trying to create a sideshow," Womack said. "We hope other people who might be inclined to consider the UAW will take this development as a cautionary tale."

Haslam's office declined to comment on the subpoena.

Other subpoena recipients include Economic Development Commissioner Bill Hagerty, House Majority Leader Gerald McCormick, state Sen. Bo Watson and House Speaker Beth Harwell.