House lawmakers on Thursday will debate legislation that would permanently expand early voting opportunities and make voting-by-mail a standard option in future elections, but Democratic leaders left out of the bill a popular reform that would allow voters to register and vote on the same day.

The latest version of the VOTES Act put together by House Ways and Means Chairman Aaron Michlewitz seeks to enshrine some of the changes made to voting rules during the COVID-19 pandemic as a way to minimize health risks. New options for voters, such as voting by mail and expanded windows for in-person early voting, led to a record number of ballots being cast in the 2020 elections.

The House bill (H 4359), however, does not call for same-day voter registration, setting up a potential clash, if that doesn't change, with the Senate where Democrats included same-day registration in the version of the VOTES Act it passed last October.

"We'll listen to the debate and see if someone changes my mind," House Speaker Ron Mariano said on Monday, regarding same-day registration. The Quincy Democrat noted that he voted against it last year when it was offered as an amendment to a broader COVID-19 relief bill, and failed.

For now, the committee bill puts some House Democrats at odds with advocates who say same-day registration could open up opportunities for younger and more transient voters. Some are alleging that House members may be trying to protect themselves from challengers, but the House might also be wary of the possibility of needing to amass the two-thirds majority needed to override a potential veto from Gov. Charlie Baker.

Baker last year knocked "the complexity" of the voting reform and the additional work it would require of local election overseers.

Advocates who see same-day registration as being critical to a final bill said Wednesday they remain hopeful that an amendment could be adopted by the full House when the committee bill goes to the floor for debate.

"We have talked to so many legislators over the past few days and same-day registration is still so popular, so we are excited about working with many members of the House on an amendment," said Geoff Foster, executive director of Common Cause Massachusetts.

Amendments to the bill were beginning to flow in on Wednesday afternoon, and Rep. Lindsay Sabadosa of Northampton filed a same-day registration amendment. MassVOTE also blasted an email to its list urging supports to call their representatives and urge them to support same-day registration.

Foster noted that at least 84 House members co-sponsored the original VOTES Act filed by Rep. John Lawn, of Watertown, which included same-day registration.

"We're hopeful the same number will stay supportive for an amendment," Foster said.

As it stands now, eligible voters must register in their city or town at least 20 days prior to an election, creating a barrier to participation, according to critics, particularly for young people and more transient populations. Same-day registration would allow unregistered but eligible voters to show up at a polling location on election day or during early voting hours, register and vote all at the same time.

Supporters say that based on data from other states the registration reform could boost turnout by as much as 10 percent across the state, and have an even bigger impact in low-income, Black and Hispanic communities. Secretary of State William Galvin, who is seeking reelection, and Attorney General Maura Healey, who is running for governor, both support the reform, as do many of the other candidates in both those races.

"It's pretty devastating to not have same-day registration in there," said Rep. Tami Gouveia, an Acton Democrat and candidate for lieutenant governor.

"We know there are a lot of ways people feel excluded from our electoral process and this is a way to allow voters to have a voice in the process, particularly knowing Massachusetts is one of the states that has more students coming to live here for four years and hopefully staying here," Gouveia said.

At least 20 states and the District of Columbia already use some type of same-day registration, including Connecticut, Vermont, New Hampshire and Maine. Senate President Karen Spilka, in a GBH radio interview on Tuesday, said Massachusetts has fallen behind.

"Too bad. We should have been number one, or earlier, but at least we should be doing it," Spilka said, adding, "I believe we should be doing anything to help people who want to vote vote."

Gouveia said that while the bill has "a lot of elements we were looking for," the exclusion of same-day registration would leave renters, students and those with inadequate housing "out in the dust.

"I think some of it is to protect incumbency. I think some of it is status quo. This is how we've always done things," Gouveia said.

The House Ways and Means Committee voted 18-8-1 to advance the bill on Thursday, with seven of the eight Republicans on the panel voting against it and Rep. Nika Elugardo of Boston casting the lone Democratic no vote. A full breakdown of the vote was not available.

Rep. Peter Durant, a Spencer Republican, said he did not feel the 45 minutes committee members were given to review and vote on the new bill was enough time.

While Durant said he was still reviewing the bill, he plans to file an amendment that would prevent cities and towns with vaccine mandates to enter certain buildings from enforcing those if they would impact someone's ability to access a polling location. Durant also said he's not necessarily opposed to same-day registration, but has concerns about its implementation and election integrity.

"What bothers me is we have no clear way of making sure voters are not registered and voting in two locations on the same day," Durant said. "We want everybody to vote, but we want them to only vote once and we want to make sure they're eligible to vote."

Ella McDonald, communications director for Act on Mass., said House lawmakers have a vested interest in resisting anything that would boost turnout among populations that could challenge their grip on their seats.

"I think it's important to look critically at the fact that in a state that has a ton of protections for incumbents and one of the lowest rates in the country of primary challengers winning elections, it's really telling that we're not able to get same-day voter registration," McDonald said.

A November 2021 poll conducted by the University of Massachusetts Amherst found that 65 percent of residents support same-day registration, compared to 28 percent who are opposed. That same poll found 64 percent in favor of voting-by-mail.

The bill would establish detailed procedures for voting-by-mail, including the dissemination and return of ballot applications and actual ballots. It would also expand in-person early voting to include all biennial state elections and primaries, presidential primaries and special elections.

Early voting in the biennial state election, which is occurring this November, would begin the third Saturday prior to the election and run through the Friday before the Election Day, while the window would shorten to the second Saturday before the election for presidential and state primaries and special elections.

Cities and towns would be directed to allow early voting during normal business hours and all weekends during the early-voting period, though the number of weekend hours required would vary based on the size of the municipality.

Finally, the bill would seek to ensure that eligible incarcerated voters are given the information and access they need to register to vote and participate in elections.