HOUSTON -

Demonstrators protesting on behalf of striking union janitors blocked the escalator at a downtown Houston office building, leading to seven arrests.

The sit-down happened Tuesday at One Allen Center on the western end of downtown Houston. A spokeswoman for the Service Employees International Union in Washington, D.C., told the Houston Chronicle that those arrested were four janitors from Chicago and three labor activists from other states.

The seven have been charged with misdemeanor trespassing. Convictions could mean up to 180 days in jail.

The 3,200 Houston-area janitors represented by the SEIU have been escalating protests and spot strikes since their contract expired May 31. More than 475 janitors in 36 buildings are now on strike for improved wages and benefits.