Three months after lawmakers enacted public pension rollbacks, a new measure has surfaced that would exempt thousands of public transportation workers from the law.

The bill's author and its union sponsors say it's a necessary, narrow and reasonable tweak to the pension statute that will keep billions of federal dollars flowing into California.

But one of the state's leading pension reform advocates said it's another example of organized labor flexing its muscle to undo the retirement changes.

"If the Legislature does this," said Dan Pellissier, president of California Pension Reform, "they're selling out to the unions."

The Teamsters and two other unions sponsored the bill, which would exclude 20,000 local and regional mass transit workers statewide from the higher pension contributions and lower retirement benefits passed last year.