From a California Dept of Education affiliated website (Jan 2010): "Although there is some variation, expenditures on salaries and benefits for all employees typically make up 80 to 85% of a district’s budget, with the bulk of it going to teachers." More here.
The California Teachers Association has been the largest lobbyist in California over the last decade and has spent more than $200 million on campaign contributions and lobbying efforts.
Teachers' unions have also been effective lobbyists at the federal level. Unions have received federal money for 400,000 jobs. According to the White House, "Additional federal aid targeted at preventing [teacher] layoffs can play a critical role in combating the [economic] crisis. Such aid would be very cost-effective. There are no hiring or setup costs...The American Recovery and Reinvestment Act of 2009 included some of this aid for 2009 and 2010. The recipient reports filled out by states and school districts show that, last quarter, Recovery Act funds supported more than 400,000 education positions. (White House blog, June 12, 2010)
For more on California politics and government unions, click HERE (Troy Senik, Fall 2009).
Update on June 2012: for a more detailed post on teachers' unions, click HERE.