OAKLAND, Calif. — Teachers in Oakland, California, walked picket lines for a second day Friday as negotiations resumed and union leaders vowed to keep pressing demands for higher pay, smaller class size and more school resources.

The strike has won resounding community support in the San Francisco Bay Area city that has become unaffordable for many of its residents.

Parents and students joined picket lines outside Oakland's 86 schools and passing cars honked in support.

Bay Area celebrities such as rapper MC Hammer, basketball star Stephen Curry and Oscar winner Mahershala Ali posted an Instagram video to say they stand with Oakland teachers.

Oakland's 3,000 teachers went on strike Thursday, the latest in a wave of teacher activism that has included walkouts in West Virginia, Denver and Los Angeles.

Union officials from the Oakland Education Association met quietly Thursday with district officials but failed to reach a deal and returned to the negotiating table Friday.

"We stand united, and our picket lines will remain strong," union President Keith Brown said.

The teachers want a 12 percent retroactive raise covering 2017 to 2020 to compensate for what they say some of the lowest salaries for public school teachers in the expensive San Francisco Bay Area.

Teachers also want smaller class sizes and say the district needs to hire more full-time nurses and school counselors.

The union has also called for the district to scrap plans to close as many as 24 schools that serve primarily African-American and Latino students. It fears more students will be lost to charter schools that drain more than $57 million a year from the district.

Salaries for Oakland teachers' start at $46,500 a year and the average salary is $63,000, according to the union. In neighboring Berkeley, a starting teacher makes $51,000 a year and the average salary is $75,000, the union said.

The union on Wednesday rejected the district's latest proposal of a 7 percent raise over four years and a one-time 1.5 percent bonus.

"We want our teachers to be fairly and justly compensated," said John Sasaki, spokesman for the Oakland Unified School District. "That said we have to do it within our financial means."

The walkout affects 36,000 students, most of whom are staying out of classrooms to show solidarity with striking teachers.