All 13 D.C. Council members have pledged to stand with 12,000 regional office cleaners preparing to go on strike and the workers’ union, Service Employees International Union, held a march down K Street during rush hour Wednesday to try draw attention to the labor dispute.

With the contract set to expire Monday, union officials say a walkout will occur at 12:01 a.m. Tuesday if an agreement is not reached on wages, hours and health benefits.

As they prepare to walk out, several hundred SEIU members joined other union advocates and members of the OccupyDC group for a 5 p.m. rally and march down parts of I and K Streets Northwest, complicating the evening commute.

After the march, D.C. Councilman Jim Graham (D-Ward 1) addressed the crowd in Farragut Square and told them the council stands behind them.

“Count on us, because we are going to work with you,” said Graham said. ”We are going to be with you.”

The dispute is part of a broader campaign by SEIU to secure new contracts for about 60,000 office cleaners in the Mid-Atlantic and Northeast.

Locally, about 5,000 office cleaners in the District, 4,000 in Northern Virginia, and 2,200 in Maryland are represented by SEIU 32BJ.

Jaime Contreras, the union’s capital-area director, predicted “there will be a lot of dirty buildings” next week if there is a strike.

“Our hope is to get an agreement, but this union has never been afraid to go on strike and we are not afraid to go on strike,” Contreras said.

The Wednesday night march on K Street, Contreras said, was “just a taste of what’s coming” if workers walk off the job.

“We are not afraid to take to the streets,” he said. “These employers, these building owners, need to see the strength of our members.”