Staff members from the offices of Reps. Ro Khanna, D-Calif., and Ilhan Omar, D-Minn., are voting on whether to unionize. It’s part of a growing movement on Capitol Hill led by the Congressional Workers Union.

The organization has been working to help offices unionize ever since the House passed a resolution to allow unionizing and collective bargaining in May. The Senate would need to pass its own resolution for organizing to be allowed in that chamber.

“While not all workplaces face the same conditions, we strongly believe that to better serve our constituents will require meaningful changes to improve retention, equity, diversity, and inclusion on Capitol Hill. That starts with having a voice in the workplace,” the organization said in a post about why they are helping the organization effort.

The office of Rep. Andy Levin, D-Mich., was the first to unionize in a unanimous vote. Now the office is showing support for other offices with pro-union posters and sticky notes on the plaque outside their door.

“The House has finally provided its workers the fundamental human right to form a union without fear of retaliation. As someone who has spent decades in the labor movement and devoted their life to protecting and enhancing workers’ rights, this moment stands out as a major highlight,”Rep. Levin said in a statement in May after his unionization resolution was approved.

The House vote fell along party lines 217-202, with all Republicans voting against the measure.