(Reuters) - Some 3,000 teachers in Oakland, California, walked off the job on Thursday in a contract dispute over salaries, class size and a proposal to close two dozen schools, the latest in a series of strikes by U.S. educators that began last year.

The Oakland Unified School District vowed to keep schools open during the strike, saying it will use central office employees, principals and temporary emergency teachers to conduct classes for the district’s 37,000 students.

The teachers’ chief demands include a 12 percent pay raise, reductions in class sizes and the hiring of more support staff such as nurses, school psychologists and guidance counselors.

The union also is opposing a plan presented by Oakland’s school superintendent in November to close as many as 24 of the district’s schools.

Union officials said the proposal follows a pattern of shutting down public schools and converting most of them to private, independently run non-district “charter schools.”

Such moves in the past, the union says, have drawn state funding away from the district while leaving its public schools shouldering the bulk of higher-cost special education classes.

HEART AND SOUL

“Students, this is a fight for your education,” union president Keith Brown said in a video on Twitter. “This fight is for the heart and soul of public education in Oakland.”

The Oakland Education Association, the union representing the city’s teachers, has been negotiating for two years with the district.

The walkout in Oakland began as teachers across West Virginia returned to school after ending a two-day strike they had called to oppose an expansion of charter schools there, clearing the way for classes to resume for about 270,000 students statewide.

West Virginia educators, among the lowest-paid in the nation, sparked a wave of U.S. teachers’ strikes last year when they walked off the job to demand higher pay. That nine-day strike ended after West Virginia agreed to a 5 percent raise.

Statewide teacher strikes last year also occurred in Arizona, Kentucky and Oklahoma. Teachers in Los Angeles, the nation’s second-largest school district, walked off the job for six class days in January in a strike over many of the same issues raised in Oakland.

A teachers strike in Denver was settled last week, ending a labor dispute that centered on demands for higher pay and a more predictable wage structure.