A deadline embedded in a ground-shaking 2021 law is looming for a dozen Greater Boston communities. Their task? Zoning reform.

Those 12 cities and towns — including Brookline, Everett and Revere — are the first that have to comply with the MBTA Communities Law. But they have been rushing to comply by year's end and have yet to submit their necessary plans. It's taken time for cities and towns to explain the law's implications and hold the town meetings and elections needed to get voters' approval. In many cases, residents say they have felt rushed into making a decision and haven't had the time to fully understand the complicated proposals.

The Baker administration and Legislature enacted the MBTA Communities Law in 2021. Although it has MBTA in its title, the law has more to do with housing than the T: it’s one of the most sweeping zoning laws adopted in Massachusetts in decades.

The law requires all 177 cities and towns in what’s considered the MBTA's service area to pass new zoning laws that will permit multifamily housing units in dense areas, largely around transit stations. Implementation of the law could allow hundreds of thousands of new housing units statewide, including 350,000 new units in Boston, Cambridge and Somerville alone.

State officials say the transit-oriented zoning would result in more walkable neighborhoods and better access to jobs, shopping, schools and other local destinations while reducing the need for people to use cars to get around. And there is an equity component according to State Rep. Andy Vargas of Haverhill. He says multifamily housing tends to serve Black and brown people, low-income people, and young people and continuing to exclude that type of zoning results in de facto segregation. The new law requires zoning districts “of reasonable size,” permitting multi family housing generally within a half-mile of transit stops and requiring a 25% increase in housing units.

Time is up sooner for the 12 cities with access to the T’s Red, Orange, Blue and Green Lines — others have until the end of 2024 or 2025. All 12 must submit what are called compliance zoning applications by the end of the year. As of publishing, none have done so, but they are continuing to debate and vote on them as the deadline approaches.

The proposal has been controversial in many communities. Some residents object to the state imposing zoning requirements on local communities and threatening to withdraw state funding if they don’t comply. There are also concerns about the growth the new housing would bring. Opponents claim there will be more traffic congestion, an increase in school population and a costly strain to the community’s infrastructure when the new multi-family housing units are built.

As in other communities, those were the issues raised before the Braintree Town Council this week.

Under the law, Braintree would be required to change its zoning code to allow for more than 3,000 new units — an increase of 25%. But Council President Meredith Boericke said building that much housing won’t happen suddenly. “The planning board will still retain oversight over how those projects are built and what the impacts would be on our infrastructure,” she said.

Boericke welcomes the new law since it could help improve many areas of town that are blighted with abandoned buildings.

”Braintree has hit a 20-year low in new growth and redevelopment,” she says, ”and the areas of town where the MBTA multifamily housing zones will be are areas that could bear some dense redevelopment.”

Following a three-hour hearing, the council voted to advance the compliance application and submit it by the end of the year deadline.

In Milton, the question of compliance is more complicated. Tim Czerwienski the Director of Planning & Community Development said there was a robust debate at Town Meeting December 11, “although the vote wound up being 67% in favor and was more support than we expected.” That decision may allow the town to meet the state’s Dec. 31 deadline to submit its compliance zoning application.

But the story may not end there. Czerwienski says there's a group of residents who say they have gathered enough signatures to call a special election in January where residents will get to vote on whether or not the article that Town Meeting passed will still stand.

“A lot is riding on that vote,” Czerwienski said.

In Newton, some feel the zoning changes approved by the City Council to increase housing in village centers may comply with the state law, but they don’t go far enough to address the city’s housing shortage. Newton's City Council approved a proposal to rezone six of its villages to allow for more housing units. A previous proposal would have targeted all 13 village centers, but the final plan passed Monday focuses only on six, which some thought was an unsatisfactory compromise.

For towns that don’t comply with the housing act, the consequences can be serious. Gov. Maura Healey has warned that non-compliant communities will have state money withheld for schools, for roads and bridges, and as she puts it, “a whole host of things that are important to communities.” And Attorney General Andrea Campbell says communities that fail to comply also risk liability under federal and state fair housing laws.

All 177 MBTA communities are required to submit an action plan that outlines the municipality’s process for adopting the compliant zoning by Dec. 31. All of them have, save one — the central Massachusetts town of Holden, which has consistently defied the law.