A three-judge appeals panel on Thursday raised serious concerns about the National Labor Relations Board’s new test for determining when a “joint employer” relationship between two companies exists for collective bargaining purposes.

The panel of the U.S. Court of Appeals for the D.C. Circuit heard arguments in Browning-Ferris Industries v. National Labor Relations Board, a case stemming from efforts by Teamsters Local 350 in California to organize workers at the company’s recycling facility that serves the city of San Jose.