The departure of Sen. Ron Calderon deprives Senate Democrats of the two-thirds margin they need in the 40-member chamber to raise taxes, pass emergency legislation, override gubernatorial vetoes and put constitutional amendments before voters without Republican cooperation.
Calderon said in a statement that he wasn't resigning but will take time to focus on fighting the charges against him.
"I do not want to distract from the important work of the Senate and my colleagues on serious issues affecting my constituents and the people of California," he said.
He said that because of the complexity of the charges, he expects a lengthy leave stretching until the end of the legislative session in August.
Calderon sent Senate President Pro Tem Darrell Steinberg the request for leave Sunday evening.
"I have accepted his request," Steinberg said in a two-sentence statement.
Calderon was arraigned last Monday on charges that he accepted bribes totaling $100,000 in cash and trips, funneling some of the money to his children.
He pleaded not guilty, but his fellow Democrats had given him until this coming Monday to resign, take leave or face being suspended.
By taking leave, Calderon will continue receiving his $95,291 annual salary but not the $163 daily expense payment he would get if he were traveling to Sacramento.
Calderon, of Montebello, is the second Senate Democrat this week to take leave while he fights criminal charges.
Sen. Roderick Wright, a Democrat who represents another Los Angeles-area district, requested the leave after he was convicted of perjury and voter fraud for lying about his legal residence. Wright is seeking to have his conviction overturned before he faces sentencing in May.
Steinberg, D-Sacramento, had said senators would suspend, but not expel, Calderon because he has not been convicted of a crime. But he and other Democrats called for Calderon to step down because he is charged with activities that Steinberg said "strike at the very heart of what it means to be a public official."
Calderon, 56, is charged with accepting bribes from an undercover FBI agent who pretended to own a Los Angeles movie studio and wanted to expand tax credits for the film industry. He also is charged with accepting bribes from the former owner of Pacific Hospital of Long Beach to back legislation involving state workers' compensation laws.
Calderon was elected to the state Senate in 2006 and represents Montebello, Bell Gardens and other southeastern Los Angeles suburbs. Wright, 61, served in the Assembly from 1996 to 2002, and has been in the Senate since 2008. He currently represents areas including Carson, Compton, Gardena, Lawndale, Hawthorne and Inglewood, though redistricting has changed the boundaries since he was accused of misrepresenting his legal residence.
The Calderon indictments threaten a powerful Democratic political family. His brother, former Assemblyman Tom Calderon, pleaded not guilty last week to eight counts of money laundering and conspiracy resulting from the same federal investigation.
With both senators gone, a spokesman for Steinberg said their staffs will remain to help deal with issues raised by their constituents, while other senators will carry on with any pending legislation they had introduced.
Calderon is termed out of office after this year, but Wright is in the middle of a term that expires in 2016. Steinberg said he expects Wright would leave the Senate if a formal conviction is entered at his sentencing May 16, meaning a special election would then be held to replace him.
Some Republicans have not been satisfied with Wright's decision to take leave instead of resigning, but Democrats blocked a move to expel him on Thursday.