According to SFGate.com, the 300,000 member California Teachers Association, which was ready to make a Clinton endorsement, pulled back. The big UTLA local is big on Obama.

Clinton’s big endorsement from the powerful California Teachers Association got upended over the weekend.
It all began Thursday when the dozen-member executive board of the teachers union - headed by Clinton ally and longtime Santa Maria educator David Sanchez - announced it had voted unanimously to back Clinton in Tuesday’s Democratic primary.
Getting the teachers’ backing would have opened up the union’s substantial checkbook to Clinton. It also would have led to mass mailings to voters, including to the union’s 360,000 members, plus the potential for major phone-bank help and other get-out-the-vote efforts on election day.
And a board endorsement almost always guarantees the membership endorsement.
But before teachers union leaders could get an up-or-down membership vote on Clinton over the weekend at a big confab in L.A., unrest broke out among the rank and file. They blocked any vote until the board’s next meeting in April - two months after Tuesday’s primary, when it really counts.
Word is, it didn’t help that Clinton’s union forces had blocked the affiliated United Teachers of Los Angeles from endorsing Obama a week earlier - and that many of its members were on hand for Saturday’s vote.