Conservative and free market groups are urging President Trump to leave empty a seat on the National Labor Relations Board, the main federal labor law enforcement agency, in order to tighten the GOP’s grip on labor policy.

The term of Mark Gaston Pearce, the Democratic appointee who currently holds the seat, term expires on Aug. 27, and Democrats have pushed Trump to re-up him for another five years. Simply leaving the seat open, however, would ensure Republican control of the board through 2020.