Service Employees International Union Local 500 has created a petition urging management at the liberal watchdog group Media Matters for America to “walk the walk” on progressive values and stop opposing the unionization of its staff. It is the latest salvo in Local 500’s nearly two-month-long effort to get MMFA to back collective bargaining.

“Employees at Media Matters have been organizing to form a union and join SEIU Local 500, but Media Matters executives have been fighting it every step of the way — even though they claim to pro-union!” the petition reads.