The NLRB argues the suit is warranted because Boeing's 2009 decision to move a production plant to South Carolina amounts to illegal retaliation against striking workers in Washington State. But Republicans charge that the suit is an open attack against right-to-work states like South Carolina on behalf of unions.

DeMint is looking for evidence that the suit was a result of coordination between the NLRB and the International Association of Machinists (IAM), and believes he has found it.

Specifically, he cited the April 2011 edition of Aero Mechanic, the newsletter of the IAM Local 751, the same local union that would benefit from the NLRB's suit against Boeing. In that edition, the group said monetary contributions "gains your Union access to officials, which is critical to get our issues addressed and ensure our input is heard."

"Local 751 would appear to be openly engaged in a pay-to-play system of political influence," DeMint said in his letter to the NLRB. "The question is unavoidable: did Local 751’s political activities or campaign contributions 'gain [it] access to officials' at the NLRB?"

DeMint's detailed FOIA request asked for all communications and documents related to the decision on an expedited basis.