A fight has broken out between the nation’s most prominent Muslim advocacy group and the labor union attempting to organize its Washington staff.

Service Employees International Union Local 500 said in filings Wednesday that the Council on American-Islamic Relations was trying to bust its effort to organize the civil rights group’s staff. CAIR responded with a statement Thursday calling the charge “meritless.” The conflict comes just days before a scheduled April 24 workplace organizing vote by CAIR’s staff.