PHOENIX (AP) — Arizona’s Republican governor on Wednesday signed a bill requiring voters to prove their citizenship to vote in a presidential election, drawing fierce opposition from voting rights advocates who say it risks affecting some 200,000 people.

The bill also requires anyone newly registering to vote to provide proof of their address.

The Legislature’s own lawyers say much of the measure is unconstitutional, directly contradicts a recent Supreme Court decision and is likely to be thrown out in court. Still, voting rights advocates worry the bill is an attempt to get back in front of the now more conservative Supreme Court.

“Election integrity means counting every lawful vote and prohibiting any attempt to illegally cast a vote,” Ducey said in a letter explaining his decision to sign the bill.

He called the bill “a balanced approach that honors Arizona’s history of making voting accessible without sacrificing security in our elections.”

Rep. Jake Hoffman, who developed the bill along with the conservative Heritage Foundation, said the measure is about eliminating opportunities for fraud, though cases of noncitizens voting are extremely rare.

The precise impact is a matter of dispute. Ducey, Hoffman and other supporters say it affects only the roughly 31,500 voters who have not shown proof of citizenship. Voting advocates say it’s vague and could go much farther, affecting hundreds of thousands of people who haven’t recently updated their voter registration or driver’s license.

“Arizona’s way out on a limb here,” said Jon Sherman, litigation director for the Fair Elections Center. “The provisions in this bill are not really found anywhere in the country.”

Arizona is the only state that requires voters to prove their citizenship when they register, a provision adopted in a 2004 ballot measure known as Proposition 200. Voters can demonstrate citizenship by providing a driver’s license or tribal ID number, or they can attach a copy of a birth certificate, passport or naturalization documents. Voters already registered at the time were grandfathered in.

In a challenge to Proposition 200, the U.S. Supreme Court ruled in 2013 that Arizona can adopt its own eligibility criteria for state elections but must accept a federal voter registration form for federal elections. The federal form requires voters to attest under penalty of perjury that they are citizens, but unlike the state form, it does not require them to provide documentary proof. The state has tried unsuccessfully to get the federal form changed.

The ruling created a class of voters who can vote only for president, U.S. House and U.S. Senate known as “federal only voters.” There are 31,500 people currently registered that way, according to the Arizona Secretary of State’s Office.

There is no evidence that the existence of federal only voters has allowed noncitizens to illegally vote, but Republican skeptics have nonetheless worked aggressively to crack down.

The bill would prohibit federal-only voters from voting by mail or voting for president. It would require state election officials to cross check registration information with various government databases.

The bill also requires people to include proof of their address with new voter registrations. Election officials say that’s complicated and unnecessary because addresses are verified at the time of voting. Voting rights advocates say it will make registration drives much more complicated, especially among people who don’t have an Arizona driver’s license or state ID with an up-to-date address, such as college students, Native Americans and seniors who no longer drive.

In a further complication, the bill would take effect 90 days after the end of the legislative session, which is likely to fall between the primary and general elections. Affected voters could vote legally in the Aug. 2 primary, would get notified their registration was at risk of cancellation if they didn’t prove their citizenship, and they’d have until Oct. 11 to fix the issue or miss their chance to vote in the general election.

Republican supporters say they plan to pass another bill delaying the start until after the 2022 election, but nothing has yet been introduced.

Sam Almy, a data analyst who consults for Democratic campaigns, said his analysis of voter registration records found just under 220,000 voters who have not updated their registration since 2004, when Proposition 200 passed. The group skews heavily toward registered Republicans, older people and those who consistently vote.

Of those affected, 71% have voted in all of the last three general elections. Forty-five percent are registered Republicans, 36% are Democrats and the rest are independents. Half are at least 65 years old and nearly 90% are at least 50.

The Arizona Motor Vehicle Division has verified that applicants for driver’s licenses and state identification cards are legally in the United States since 1996 but does not verify that they’re citizens, said Bill Lamoreaux, an agency spokesman. There are about 192,000 people with a state license or ID issued before 1996, he said.

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