The California Supreme Court on Friday upheld the state Senate maps drawn last year by an independent redistricting commission, dealing a blow to GOP attempts to block Democrats from gaining enough seats to pass taxes on their own.

The high court announced that the Senate maps drawn by the citizens commission should be used in the June primary and November general election, even though an initiative challenging the map is expected to qualify for the ballot.

Republicans are seeking an initiative to overturn the new boundaries and wanted the new maps tossed out until voters decide the issue. The court first had to find whether it even had the authority to act because the GOP initiative has yet to qualify.

The court found that the maps drawn by the California Citizens Redistricting Commission were "clearly the most appropriate map to be used in the 2012 state Senate elections even if the proposed referendum qualifies for the ballot."

Republicans stand to lose seats to Democrats under the Senate maps because of the state's shifting demographics, giving them a better chance of reaching a critical two-thirds majority in the Senate. That would bring Democrats a step closer to being able to approve tax increases without Republican support in one house of the Legislature.

Orange County Republican activist Julie Vandermost filed the lawsuit in October. She and GOP interests contend the commission did not meet the constitutional criteria for drawing the maps in a transparent way and in trying to keep communities together, violating the federal Voting Rights Act.

Neither the California Republican Party nor the redistricting commission had an immediate response to Friday's ruling.

The Supreme Court justices had several options in considering the case: They could allow the temporary use of the redistricting commission's maps; use the state Senate districts that have been in place since 2001; devise an alternate plan; or create temporary Senate districts out of pairs of Assembly districts drawn by the commission.

The 40-member Senate has half the number of lawmakers as the Assembly, where any change in the balance of power is less certain under the newly drawn political boundaries.