"This is an action to get the attention of the mayor. We've tried every other way we can," said Brenda Barros, a nursing assistant.
They started off within earshot of Mayor Gavin Newsom's office. SEIU represents nursing assistants, clerical workers and other city employees. They say 500 jobs are on the line because of budget cuts.
At Market Street hundreds rallied on the sidewalks, while a small contingent gathered in the middle of the intersection surrounding a sign reading "We will not step back."
Reportedly in the crowd were some of the very people whose job is to keep traffic moving.
ABC7 heard that some parking control officers are taking part in the demonstration. In response, Barros said "We represent all miscellaneous city employees, so there could be people from anywhere in the city in this demonstration."
According to police, 18 people were arrested and cited for an infraction of obstructing traffic and then released.
On Tuesday, the action moves to City Hall where legislation sponsored by Supervisors John Avalos and Chris Daly will be debated. It would take money from the Department of Public Health to prevent the layoffs.
Daly says the proposed cuts he is fighting target certain workers.
"Frontline workers are disproportionately people of color. What we haven't seen in terms of dealing with this budget crisis is we haven't seen managers, who trend white, cut," said Daly.
Monday night the mayor's office released a statement saying the supervisors' proposal "?would result in layoffs elsewhere," and that "?[due to] a $522 million deficit next year, people should unfortunately be prepared for even more layoffs."