Students 21 and over may find they are denied access to local bars — even though they are legally of age to consume alcohol — if they lack a Massachusetts-issued identification card.

Mary Ann’s, a Brighton-area bar popular with Boston College students, recently implemented an ID policy that strictly denies the use of any out-of-state IDs without exceptions following several incidents involving underage drinkers using fake IDs.

The new policy comes at the suggestion of the local liquor licensing board, after citations following repeated instances of underage drinkers being served at the bar.

Subsequent violations would force the bar to close by 11 p.m. — which would be devastating for a business that thrives at night.

Yet even in keeping their late hours, Mary Ann’s faces an uphill battle to hold on to their clientele, which is now limited to customers with Massachusetts IDs, valid passports or military identification. According to an anonymous Mary Ann’s employee, quoted by The Heights, the bar has lost roughly half its business because of the new policy.

According to Massachusetts law, alcohol licensees that do not comply with all state laws face having their license suspended, cancelled, modified or revoked. Local liquor licensing boards have the authority to take action as they see fit, such as revoking a license or scaling back hours, as in the case of Mary Ann’s, depending on the circumstances.

State laws for using fake IDs can carry penalties ranging from a fine to three months incarceration. Using fake motor vehicle identification is a felony, and can carry a sentence of up to five years in state prison.

Mary Ann’s drastic rule changes have left some bar owners perplexed.

Angus O’Leary, owner of the Brookline bar O’Leary’s, said he and his staff have had no problems keeping underage drinkers out while still accepting out-of-state IDs.

“We use an official publication that serves as an ID guide [for identifying non-Massachusetts IDs],” he said, adding that the bar’s patrons consist mostly of local regulars.

O’Leary said he suspects that the decision to enforce a new ID policy at Mary Ann’s came merely at the suggestion of the liquor licensing board.

“I think you can make an inference from [the suggestion],” he said.

Steve DeMarco, proprietor of T’s Pub, sympathizes with Mary Ann’s. “You got to do what you got to do,” he said. “You got to be careful because everybody tries to get in.”

DeMarco said the current identification card system should be reformed to solve the problem of illegal ID use in Boston.

“I think there should be one form of public identification for the whole country,” he said, adding, “If you’re old enough to fight for your country you should be able to drink.”

Joe Caliguiri, a 21-year-old New York native and COM senior, expressed surprise at Mary Ann’s policy and the apparent conflict between Massachusetts state and national alcohol policies.

“I thought that 21-and-over alcohol laws were federal laws,” he said. “How can Boston supercede them?”

Caliguiri also noted that other city bars have never questioned him about his New York license, but he could imagine bars in his home state possibly enforcing a similar policy.