The benchmark approaches.

Next week, the first big deadline for the MBTA Communities law — the 2021 legislation that mandates cities and towns with access to the MBTA to zone for new multifamily housing — will arrive. Each of the 175 communities subject to the law are required to submit an “action plan’’ to the Department of Housing and Community Development by Jan. 31, outlining how they’ll go about their up-zoning.

Beyond the actual plans, the deadline will also serve as a litmus test for how communities — their leaders and residents — are feeling about playing their part in the state’s most ambitious housing effort in decades.

If towns play along, the law would enable hundreds of thousands of units of housing, but some communities have signaled skepticism and publicly considered the consequences of noncompliance. The Globe reported last month that DHCD is cutting the budgets of housing authorities in noncompliant towns, which some advocates say, while harsh, may help prod them into following along.

Next week’s deadline may shine some light on which communities are still balking — even though all that’s required at this point is to fill out a relatively simple six-page form.

Detail a strategy

While the paperwork is simple, the zoning changes the law mandates can be big, big enough to spark complex conversations that could ensnare towns and cities for years.

The state knows that, said Clark Ziegler, executive director of the Massachusetts Housing Partnership, and wants communities to chart a plan for how they’ll accomplish the mandated changes over this year and beyond.

Will they change the zoning requirements on an existing district to allow for multifamily building? Zone a new district entirely? The state is hoping communities have already begun to consider this question, and wants them to indicate what they’re thinking about on their action plan.

“We know this is a big lift,’’ said Ziegler. “That’s why we want communities to get out in front of this.’’

Ziegler said MHP, along with a number of other advocacy groups and agencies, is offering on-the-ground technical assistance to help work through the process and come up with districts that satisfy the law.

Outline existing districts that could potentially be rezoned

A question that has repeatedly bubbled up among city and town leaders is: “What if we’ve already created multifamily districts near transit?’’

Take a city like Revere, which has a line of towering apartment buildings near the Revere Beach and Wonderland Blue Line stops. Do officials there need to create another multifamily district?

Some towns have thousands of multifamily units that were built under special permits to circumvent local zoning, as opposed to being allowed by-right — as is required by MBTA Communities. How do they come into compliance?

The answers in those situations aren’t immediately clear, but the state is planning for it, said Ziegler. In their action plans, officials must indicate if they have a district already in place that they think could satisfy the MBTA Communities requirements.

Then as they work toward new zoning, town planners will have to figure out if those zones actually qualify. DHCD has created a compliance tool that allows planners to enter the parameters of a specific zone, like dimensional restrictions and parking requirements, to see if it passes muster.

Establish a timeline

It may seem simple, but a timeline could be crucial to getting communities to actually finish their new zoning, advocates say.

New zoning rules can be highly controversial on the local level, and changes much smaller than what MBTA Communities mandates sometimes take years to pass.

The region’s rapid transit communities — the cities and towns whose rezoning will have to allow for the most units, in a few cases more than 10,000 — must complete their new zoning by the end of the year. That’s a tight turnaround, and advocates say incremental goals and deadlines, which the state wants communities to outline in their action plans, will help leaders get the zoning passed on time.

“We’re confident we can get this done,’’ said Ziegler.

Andrew Brinker can be reached at andrew.brinker@globe.com.