The Council on American-Islamic Relations (CAIR), an influential Muslim advocacy group, is fighting efforts by the Service Employees International Union (SEIU) to unionize its staff.

SEIU Local 500, which represents 20,000 teachers, health care workers and non-profit employees in Washington, D.C. and Maryland, submitted union authorization cards that were filled out by over half of CAIR’s eligible staff, Christopher Honey, communications director for SEIU Local 500 told The Daily Caller News Foundation Tuesday.

CAIR appealed to the National Labor Relations Board (NLRB), according to the Washington Examiner, arguing that it is a religious organization and therefore exempt from the National Labor Relations Act (NLRA). Congress passed the NLRA in 1935, which protected the rights of employees to organize under a union but included exemptions, including one for religious organizations.

The NLRB’s Region 05 rejected CAIR’s argument Friday, asserting the the group is primarily a civil rights organization, not a religious one. The NLRB also set April 24 as the date for employees to vote on whether or not to join the SEIU Local 500 chapter.