SAN BRUNO (CBS/AP) – School districts in California have issued nearly 19,000 layoff notices so far to teachers amid uncertainty over the state budget, the California Teachers Association estimated Tuesday.

The union announced its estimate of preliminary notices on the day school districts must let employees know they could lose their jobs.

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Some districts had yet to fully report how many warnings had been distributed as they prepare for worst-case budget scenarios.  The union said it expects to have a final count Friday.

Its early estimate includes almost 500 school employees in San Francisco, 540 in Oakland, nearly 900 in San Diego, and about 5,000 educators in Los Angeles.

The situation is not unique to California. School districts throughout the country are warning of cutbacks involving teacher and other employees, as state legislatures seek to close massive budget shortfalls by cutting education spending.

Not all of the estimated layoffs will be carried out in California.

Schools have until May 15 to issue final layoff notices. Two years ago, districts handed out layoff notices to a record 26,500 teachers, but only 60 percent of them ended up losing their jobs.

Meanwhile, teachers and parents rallied around the state Tuesday to drum up support for Gov. Jerry Brown’s budget proposal.

Brown’s plan for closing the state’s nearly $27 billion budget deficit seeks to maintain current K-12 spending levels by asking voters to extend temporary increases in the sales, personal income and vehicle taxes for five years.

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But so far the governor has not secured enough Republican support to hold a special tax election.

Without the tax extensions, school districts would face another round of deep budget cuts that education officials warn would prompt widespread layoffs and campus closures.

In Union City, between San Jose and Oakland, kindergarten teacher Quyen Tran was one of about 60 school employees in her small school district to get a layoff notice. She started teaching in New Haven Unified School District in 2006.

Quyen, 30, said she was laid off last spring but hired in August right before the school year began. She is expecting her first child in June.

“It’s very stressful,” she said during a news conference, “just not knowing where I’m going to be next year or how secure my income will be.”

Quyen, however, said she’s more worried about the impact of state budget cuts on her students.

“With all these layoffs of teachers, they will have no choice but to stuff more kids into these classrooms,” she said. “They’re going to be cheated out of their education just because there are not going to be enough teachers around.”

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