Sen. Bernie Sanders (I-Vt.) on Friday endorsed a teachers' strike in Oakland calling for improved working conditions.

The Democratic presidential candidate voiced support a day after teachers began striking for higher wages, smaller class sizes, more counselors and nurses for students, and a halt on school closures that have ramped up due to budget cuts.

Around 3,000 members of the Oakland Education Association (OEA) began picketing Thursday outside 86 schools in the Oakland Unified School District.

"I stand with @OaklandEA teachers who are fighting for smaller class sizes, fairer pay, more student support, and fundamentally defending public education. Oakland must not shut down 24 of the city's 87 public schools," Sanders tweeted.

The school district's Board of Education announced in November it would proceed with a "community of schools policy" that could shutter as many as 24 of the district's schools over the next several years to cope with budget cuts and inequality across the district, according to the Oakland Post.

"The educators' union sees this strike as a fight for a better future for Oakland's 37,000 students, rather than the traditional give and take over wages and benefits for educators," OEA President Keith Brown said in a statement, adding that "you can't feed the minds of our students by starving their schools."

The teachers are also demanding a 12 percent bump in their wages over the next three years. Teachers in the school district are among the lowest paid in the country, with Edsource.org estimating the average salary to be $46,411.

Some Oakland teachers also organized a one-day protest in December, saying their salaries were inadequate to cover the high cost of living the San Francisco Bay Area.

Sanders announced Tuesday that he would launch a second White House bid after his 2016 run, joining fellow Democratic candidates Sens. Kamala Harris (Calif.), Elizabeth Warren (Mass.), Cory Booker (N.J.) and Amy Klobuchar (Minn.), among others.