SACRAMENTO, Calif. (AP) — California lawmakers leading an effort to extend the state’s signature climate change initiative made a last-minute appeal Saturday to critics on the left who say their plan doesn’t do enough to reign in polluters.

The unusual weekend conference call with reporters underscores the trouble facing Gov. Jerry Brown and his legislative allies as they try to shore up support for the program they call a model for the world. It follows the introduction of legislation that may make the deal more appealing to Republicans.

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Lawmakers are scheduled to vote Monday on bills that would extend the program while requiring air-quality monitoring and improvements in the most polluted neighborhoods.

“I don’t know that we’re going to have another opportunity like this to really move the ball forward on clean air and be a model not just for California but for the rest of the world,” said Assemblywoman Cristina Garcia, a Los Angeles area Democrat and author of the air-quality measure.

California’s cap and trade program puts a limit on carbon emissions and requires polluters to obtain permits to release greenhouse gases. The program expires in 2020 unless lawmakers take action, and Brown says extending it now will give companies the certainty they need to efficiently respond.

Cap and trade has long been debated among environmentalists. Some favor it as a market-based program that gives polluters the incentives and flexibility to find the most cost-effective ways to reduce greenhouse gas emissions. Others say it gives too much leeway to allow oil refineries, factories and other polluters to continue releasing toxic gases that are particularly harmful to people living in the immediate vicinity.

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Garcia, who represents an area of southern Los Angeles County choked by dirty air, has fought to link local air-quality improvements with any extension of cap and trade. In Saturday’s conference call, Garcia said the air-quality improvements she advocates can’t succeed without the money generated by cap and trade.

The Saturday plea comes less than a day after the top Assembly Republican introduced legislation that may be designed to pick up support on the right. The legislation by Assembly Chad Mayes, R-Yucca Valley, would require a one-time supermajority vote to spend revenue from cap and trade pollution permits collected after 2023. That would likely increase the voice of Republicans and moderate Democrats in how the revenue — which amounts to hundreds of millions of dollars a year — is spent.

The provision requires voter approval.

It’s not clear if the legislation is enough to pick up support from Republicans. Garcia and Assemblyman Eduardo Garcia, a Coachella Democrat who is the lead author of the cap and trade extension, said Saturday that they were unaware of the GOP bill.

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