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TRENTON, N.J. (CBS/AP) — Some lawmakers and county officials are warning a new law enacted last month that’s changing New Jersey’s vote-by-mail system could spark confusion.

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Democratic Gov. Phil Murphy signed the new law in August, and it’s going into effect in time for this year’s closely watched midterm elections, in which one Senate seat and all 12 House posts are on the ballot.

Under the law, voters who requested mail-in ballots for all future elections will continue to get them until they opt out. That’s a change from previous law that required officials to check in with mail-in voters to ask if they want to continue after the fourth general election since they signed up.

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But the law also made another change, which clerks say has resulted in frustration and a dash to inform voters about their status.

The new law mandates that voters who signed up for and got mail-in ballots for the 2016 general election will continue to be sent those ballots for all future elections, unless they opt out.

That means that voters who wanted to vote absentee in 2016 but expected to vote at a machine this year in person might be surprised when they turn up at the polls.

That’s resulted in the state’s clerks mailing letters to voters notifying them of the change and giving them a chance to opt out. The message to those voters, say lawmakers? Check your mail.

The change raises the possibility that voters will be confused and could question the legitimacy of the system, according to Republican Sen. Declan O’Scanlon who voted against the bill.

“Whenever someone shows up to the polls and is not permitted to cast their vote — they go nuts. It’s upsetting,” he said. “It’s embarrassing. They suspect something nefarious is going on.”

Supporters of the bill say it expands voter participation by giving more voters a chance to participate earlier than just on election day, and from the convenience of home in many cases.

“Governor Murphy believes that no voter should be disenfranchised,” Murphy spokeswoman Alyana Alfaro said in a statement. “Expanded vote by mail is a critical step that will help ensure that all eligible voters are able to participate in the democratic process.”

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For the state’s 21 county clerks, which handle mailing out ballots, implementing the new law has been a struggle.

The New Jersey Association of Counties is considering filing a complaint about the new law and the unfunded mandate that it’s set up, said the group’s executive director John Donnadio.

Monmouth County Clerk Christine Hanlon, a Republican, called the new law her “nemesis,” and said she’s had to supplement her staff of four this year to 10 by adding people from other county government divisions. She likened the level of activity to a presidential year, when turnout is much higher.

But, she added, voters should be concerned about their vote counting.

“We are going to get it done,” she said. “One way or another if you wanted to vote, you will be able to vote.”

Democratic Camden County Clerk Joe Ripa, though, embraced the change. He says voters complained to him about the “onerous” opt-out requirement under previous law.

“This new procedure is ideal for residents and I’m happy this pragmatic fix is finally being applied to pave the way for additional access to the democratic process,” he said in a statement.

Voters affected by the change who did not opt out of mail-in voting can vote by provisional ballot at their polling place.

New Jersey is one of 27 states that permit voters to get mail-in — sometimes called absentee — ballots without any excuse, according to the National Conference of State Legislatures. Neighboring New York and Pennsylvania, unlike New Jersey, require a rationale for absentee voting and do not permit voters to cast ballots early.

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It’s unclear exactly how many people will be affected by the new law. In 2016 about 356,000 voted by mail-in ballot, or 9 percent of the total number of ballots cast.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)