SAN FRANCISCO (CBS SF) — Tax day turned into protest day in San Francisco, as dozens of city workers and others gathered at City Hall for a march to decry tax breaks for Twitter outside the company’s headquarters on Market Street Tuesday.

It was a well coordinated march that included a flat-bed truck and a speaker system.

Service Employees International Union (SEIU) members in their purple shirts donned Mayor Ed Lee mustaches and are upset with the Mayor’s agreement three years ago with some tech companies in the city that was a plan to attract business to the Mid-Market area.

“We don’t understand why this mayor can’t go to tech companies and say, ‘you’re doing fine. The economy is working for you. I want to renegotiate the tax breaks.’ He can do it, the question is will on his part,” said union member Larry Bradshaw.

Susan Gard with the Department of Resources, which is responsible for negotiating with the unions on behalf of San Francisco, said the targeting of Twitter is a “smokescreen” for the package the union has put on the table. It’s a package she called “outrageous”.

“SEIU are asking for a lot of things that are just unreasonable and unaffordable. The proposals they put on the table would cost the city city almost $300 million.”

The union’s contract expires in June. If an agreement can’t be reached the two sides will head to binding arbitration.

Protesters say the city is losing out on hundreds of millions of dollars by giving tax breaks to big name companies.

Twitter alone received over $50 million in tax breaks last year from the city.