National Labor Relations Board Chairman John Ring warned this week that recent actions by Senate Democrats create the appearance that they are trying to “improperly influence” a major case the board is trying resolve involving McDonald’s Corp.

The Democrats on the Senate Health, Education, Labor and Pensions Committee have been asking whether Ring and another NLRB boardmember, William Emanuel, would recuse themselves from the case. In a letter to leaders of that committee, Ring accused Democrats of using pressure tactics against his board.