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CHICAGO — Chicago teachers and supporters flooded the streets of downtown Chicago during the busy afternoon rush as part of today’s “Day of Action.”

Teachers in the nation’s third-largest district are launching an unprecedented one-day strike. They say it’s aimed at getting lawmakers to adequately fund education and other programs.

Several streets in The Loop were temporarily block to traffic as the large crowd marched from the Thompson Center.

CPS filed a charge against the teachers union calling today’s one-day strike “illegal.”

In a filing to the Illinois Educational Labor Relations Board, CPS says the Chicago Teachers Union strike does not follow the state law governing teacher strikes.

The district sees unspecified damages and an order prohibiting any future strikes from occurring outside the state law.

CPS CEO Forrest Claypool said at a news conference that the district wants a “permanent, pre-emptive injunction” against similar strikes in the future.

CTU responded saying they disagree.

The Supreme Court 60 years ago authorized unfair labor practice strikes under the National Labor Relations Action and we believe teachers have those rights. This was a one day job action. Their charges were filed after the fact and they seek to enjoin us from doing something have no intention of doing again. We call on CPS to join us in fighting for more revenue for schools.

The walkout closed schools for nearly 400,000 students who will have the option of spending the day at one of the “contingency sites” Chicago Public Schools is opening at churches, libraries and school buildings.

CTU last went on strike in 2012, shutting down schools for more than a week before reaching an agreement with Mayor Rahm Emanuel. That contract expired in June.

Friday’s action could foreshadow a longer strike over a new contract, which by law can’t occur for several weeks.

CPS officials say teachers who strike will not get paid for the day and sick days cannot be used.

The union has warned teachers who cross the picket lines that they will be disciplined.

The CTA is offering free rides to CPS students to accommodate those who have to travel to contingency sites because of the strike.

Students will be allowed to ride trains and buses for free between 5:30 a.m. and 8:30 p.m. today.

Not only are Chicago teachers staging a one-day strike, but fast- food workers joined them demanding a $15 minimum wage.

Students, teachers and fast food workers marched from the Roosevelt school on the Northwest Side to a nearby McDonald’s to get their message across.