The controversial MBTA Communities Act is a constitutional law that the attorney general can enforce with legal action, but the measure remains “ineffective” until the Healey administration takes another pass at crafting regulations, the state’s highest court ruled last week.

In a 23-page decision rife with implications for state efforts to influence housing affordability by facilitating more housing production, the Supreme Judicial Court ruled the 2021 zoning reform law does not run afoul of the state Constitution and that Attorney General Andrea Campbell is allowed to sue cities and towns that fail to comply.

However, the court found that the Executive Office of Housing and Livable Communities did not follow state law when promulgating relevant guidelines, rendering them “presently unenforceable.”

Gov. Healey and her deputies praised the decision upholding the law, and said they would move to craft new emergency regulations by the end of the week to plug the gap opened up by the ruling.

Campbell, who sought to enforce the law against Milton and also defended its constitutionality in court, called the decision “a resounding victory for the Commonwealth and a major step forward in our work to address the unacceptably high cost of housing for our residents.”

Kevin Martin, an attorney who represented Milton in the legal proceedings, said town officials are “very pleased the Court recognized the critical importance” of mandatory regulatory steps.

“In that respect today’s decision was a victory not only for Milton but also the rule of law,” Martin said in a statement. “We hope that in issuing new guidelines, the Executive Office takes account of the many serious substantive concerns raised not only by Milton, but also by other affected communities.”

The ruling sets a major precedent affecting close to half of the state’s cities and towns, and it drew support from organizations representing tenants, real estate industry leaders and more. Groups that issued statements of praise included Associated Industries of Massachusetts, the Metropolitan Area Planning Council, the Greater Boston Real Estate Board and Homes for All Massachusetts.

Most cities and towns subject to the MBTA Communities Act have already complied with the mandatory zoning changes. Opponents view the law as unnecessarily heavy-handed, voicing fears that allowing more multifamily housing by right will impact neighborhood character.

More than two dozen cities and towns that have hesitated to enact the required zoning changes or outright resisted the mandate will now need to come into compliance, but the timeline is unclear.

Sam Drysdale, Sam Doran and Colin A. Young contributed to this report.