A coalition of conservative groups urged Senate lawmakers to oppose the renomination of Mark Gaston Pearce to the National Labor Relations Board, the main federal labor enforcement agency, saying that Pearce was responsible during his tenure as chairman for turning the NLRB into a partisan entity rather than a neutral arbiter of policy.

The plea comes as pressure is being brought to bear by Democratic lawmakers to get two of Trump's appointees to the five-member board, Chairman John Ring and William Emanuel, to recuse themselves from a wide swath of cases, a move that would functionally give the board a Democratic majority if Pearce stayed on.

"Congress should not re-appoint Pearce to another term. All stakeholders governed by the NLRB — workers, employers, and unions — deserve better than an NLRB member who ignores facts and issues decisions that are legally unsupportable and economically harmful," said the coalition, which includes Heritage Action, FreedomWorks, the Club for Growth, and the Competitive Enterprise Institute, among others. The letter was directed to the Senate Health, Education, Labor and Pensions Committee.

The five-member NLRB is a quasi-independent agency. The board’s members are appointed by the president and confirmed by the Senate. By tradition, the president picks the majority but allows the opposing party to have the remaining two seats. It currently has a controlling 3-1 GOP majority, with one seat open since Pearce’s term, which started in 2010, expired in late August. Trump has reportedly worked out a deal with Senate Democratic Leader Chuck Schumer, D-N.Y., to get other presidential nominees approved in exchange for approving Pearce's continuing on at the NLRB.

Conservative and pro-business groups have been lobbying the White House to find somebody other than Pearce to fill the open slot. In Tuesday's letter the groups argued that he was partly responsible for the pressure on Ring and Emanuel to recuse themselves. "Pearce played a part in the weaponization of ethics rules at the NLRB — using ethics rules on conflicts of interest to wrongfully pressure certain Board members into recusing themselves from important cases. Those misdeeds by Pearce and his allies have improperly cast doubt on the agency and frustrated the Board from administering the National Labor Relations Act," they argued.

A White House spokesperson could not be reached for comment.