After seven weeks of frantic work by county officials to meet a Saturday deadline, New Jersey voters are starting to receive mail-in ballots under a new state law.

That law, signed Aug. 10 by Democratic Gov. Phil Murphy, made big changes to who receives mail-in ballots ahead of the Nov. 6 midterm elections, which will determine whether Republicans retain control of Congress.

New Jersey is home to four Republican-held congressional districts that Democrats believe they have a good chance of flipping this fall. They need to pick up 23 such seats nationally to secure a majority in the U.S. House of Representatives.

U.S. Sen Bob Menendez, D-N.J., is also on the ballot and facing a well-funded challenger in Republican Bob Hugin. The race could have major implications for a narrowly divided Senate.

Here’s what you need to know about the new law.

What changed?

Anyone who voted by mail-in ballot in the 2016 general election, which pitted Donald Trump against Hillary Clinton, has been automatically enrolled to receive mail-in ballots for every election going forward unless he or she opts out. That includes the 2018 midterms.

The change affects the more than 350,000 residents who voted by mail in 2016.

Voters who did not use a mail-in ballot in 2016 but want to going forward can also sign up to take advantage of the new law. Previously, voters could only sign up to receive mail-in ballots for a single election, every election in a calendar year or every general election going forward, said Mary Melfi, the Hunterdon County clerk and president of the New Jersey Association of Counties.

Am I affected?

Clerks in all 21 counties sent letters to affected voters in recent weeks informing them of the change and giving them a chance to opt out. The opportunity to opt out for the Nov. 6 election has passed, as clerks have to send out the first round of mail-in ballots by Saturday.

For those unsure whether they were affected, county election officials can answer your questions. The state has published the contact information for election officials in every county.

What if I don’t want to vote via mail-in ballot?

If voters are enrolled to receive a mail-in ballot but show up at a polling place on Election Day anyway, they will still be allowed to vote. Instead of voting on an electronic voting machine, however, poll workers will ask these voters to fill out a provisional ballot.

All voters’ names will still appear in the voter rolls, and votes cast via provisional ballots will be counted the same as those cast on a voting machine or using a mail-in ballot.

Why the change?

Democrats who control the Legislature used their numbers to pass the measure despite nearly uniform Republican opposition. Supporters say the legislation will help increase voter turnout, especially during midterm years when participation dips compared to presidential election years.

“Vote by mail has been a successful method for increasing voter participation for quite some time and it is being used in other states, in other countries and in many counties in New Jersey,” Sen. James Beach, D-Camden, a prime sponsor of the legislation, said in a statement Thursday. “It increases voter turnout and is especially helpful for senior citizens and the disabled and for voters with demanding schedules managing work and family responsibilities.”

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Does the law favor Democrats?

In New Jersey, where Democrats have 900,000 more registered voters than Republicans, greater voter participation using mail-in ballots would generally give Democrats a boost, said Patrick Murray, director of the Monmouth University poll.

“If you get more voters to sign up for automatic mail ballots, they’re more likely to send them back,” Murray explained. “And because there are numerically more Democratic voters in New Jersey, particularly with a more active Democratic get-out-the-vote operation, you’re going to get more of those voters to be Democrats.”

Murray added that Democrats in the past have not had the success they would like with early voting, in part because they had to start the process over each year of signing many people up for mail-in ballots. The new law changes that.

Did county clerks have enough time to implement the law?

Beach, the bill sponsor, said the change “was not new to election officials and it came as no surprise.” But several clerks said they thought the law would take effect after the November elections and had to scramble to implement it between the time Murphy signed it in August and Saturday’s deadline.

County staff worked around the clock to identify affected voters, update forms and send out letters. All told, county offices spent more than $1 million in overtime, printing, temporary help and postage implementing the new law, according to a survey conducted by the New Jersey Association of Counties.

John Donnadio, the association’s executive director, said the organization’s lawyers are exploring whether they can file a complaint with the state Council on Local Mandates seeking state reimbursement for the expenses.

Can I still register to vote?

Yes. The deadline to register to vote in the midterm elections is Oct. 16.

More information on how to register to vote, and to check if you are already registered, is available on the state website.

Email: pugliese@northjersey.com