The United Automobile Workers has seized on leaked documents from Gov. Bill Haslam of Tennessee in its efforts to persuade the National Labor Relations Board to order a new unionization election at the Volkswagen plant in Chattanooga.

The union, which lost a vote in February, plans to argue in a hearing later this month that Mr. Haslam and Senator Bob Corker of Tennessee, both Republicans, frightened VW workers at the plant with anti-union statements that made a fair vote impossible. The board’s director for the region that includes much of the Southeast has set the hearing for April 21.

In the documents, revealed earlier this week, Mr. Haslam proposed nearly $300 million in incentives to help the VW plant add a second production line, contingent on the unionization effort’s “being concluded to the satisfaction of the state.” The documents, including the outlined incentives, were made public Monday by WTVF, a Nashville television station.

Bob King, the U.A.W.’s president, said in an interview on Friday that the documents showed that Mr. Haslam was improperly trying to pressure VW to oppose unionization and was signaling to workers that their plant would not obtain the subsidies needed to expand if they voted to join the union.