Sanders supporters reportedly suing to have California's voter registration extended until primary day

A California lawyer reportedly is asking a federal judge to extend voter registration past the Monday deadline, alleging the state’s rules on the June 7 presidential primary is causing widespread confusion.

The presidential contests are controlled by the state’s Democratic and Republican parties, unlike statewide primaries in which voters can choose any candidate regardless of their political party, according to The Los Angeles Times, which first reported the story.

Democrats have opened their primary between front-runner Hillary Clinton and Vermont Sen. Bernie Sanders to voters who have no political affiliation.

However, the lawsuit alleges that elections officials in some of California's 58 counties aren't making that provision clear to unaffiliated voters.

Supporters of Sanders, whose candidacy has been boosted in other states by independent voters, are focused on the state's so-called "no party preference" voters, considering they account for roughly one-quarter of the state’s registered electorate.

According to the paper, Sanders volunteers were announcing to the crowd going into a campaign rally last week in Carson, Calif., that they had to be registered as either unaffiliated or a Democrat to vote. And those who were not were given step-by-step instructions about the process.

The suit was filed Friday by Oakland civil rights attorney William Simpich, according to The Los Angeles Times.

He said a judge should require state elections officials to conduct a broad public-awareness campaign about the voting rules before May 31, the deadline for requesting a ballot by mail. And he wants voter registration to be extended through the June 7 balloting.

Clinton only needs about 90 of the 939 delegates still available in their party’s remaining seven contests to clinch the nomination, with 475 of them at stake in California.

The Republican Party did not open its California presidential primary, in which Donald Trump is running uncontested, to unaffiliated voters.

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