Jack MacMaster has 10 grandchildren. He wants to buy presents for them. But for the past three years, his disposable income has shrunk to a tiny amount, usually just $100 each month.

“When the holidays come, birthdays — I can’t afford to buy anything,” he said. “I can’t tell you the last time that I was able to afford a new shirt or slacks.”

Since he moved into Prospect House, an assisted living facility in Revere, he has been charged “ancillary fees” in addition to his rent, leaving him with very little leftover for all other expenses. He’s not the only one.

MacMaster and several other low-income disabled residents at Prospect House have joined a class action lawsuit recently filed in U.S. District Court in Massachusetts, alleging that the fees that they are being charged are a violation of state and federal housing laws. They want answers.

“There’s so many people there that [have] no idea what they’re paying for,” MacMaster said.

Sean Ahern, a senior attorney at Greater Boston Legal Services, which is bringing the suit, says that it’s unclear what the fees are for that is not already paid for from separate sources.

“It seems to be that this is an arbitrary and unfair and deceptive fee,” Ahern said. “The fees are very, very oppressive in terms of their impact on the residents and their ability to navigate life day to day.”

Prospect House is managed by HallKeen Management, Inc., based in Norwood. Because it is part of the Low-Income Housing Tax Credit program, rents are capped for many of its units, which some residents pay for with social security. The ancillary fees take nearly all of the residents’ leftover income.

MacMaster and other residents are part of the Program of All-Inclusive Care for the Elderly (PACE), through MassHealth and Medicare, which provides low-income older adults with support so that they can live in the community. The PACE Program pays Prospect House for services like meals, dressing, bathing and cleaning.

The lawsuit argues that because of Prospect House’s involvement in those federal and state programs, the fees are a violation.

“They can’t charge any mandatory fees in addition to the maximum rents,” Ahern said. “So that all begs the question of, so what is the ancillary charge and what is it going toward?”

Ahern notes that the fees vary from person to person, and don’t correlate to more or less services. The fees change from year-to-year for individuals when their federal benefits are adjusted — and however they change, it leaves each resident with just $100 in their pocket each month.

According to the lawsuit, the company does not charge the fees at its other locations, which they argue means the fees are unfairly being applied to people with disabilities.

MacMaster is 76. He lost his right leg to vascular disease after moving into Prospect House and uses a wheelchair to get around. He says he is happy with the support he gets at the facility. Staff help him get out of the bed in the morning, as well as take trash out and stay on top of his medications. He does his own housekeeping and laundry and showers and gets dressed himself.

But MacMaster says the limited money in residents’ pockets is taking a toll on them.

“There’s one gentleman who, he can’t afford razor blades or shaving cream. So I invite him down here and I cut his beard for him,” MacMaster said.

In response to questions from GBH News, HallKeen officials defended their care of low-income residents. They said that the fees are “for additional services.”

“We believe firmly that our policies are compliant with all applicable statutes as well as being consistent with assisted living industry standards,” HallKeen said in a statement. “Since these issues were raised earlier this year, we have worked actively and in good faith with Prospect House residents and with the Commonwealth’s Executive Office of Elder Affairs and the Executive Office of Housing and Livable Communities, and we also are implementing changes to our leasing agreements and other internal protocols to further clarify our policies.”

The inability to pay those extra fees has meant that some residents have either left the facility or faced eviction. MacMaster had an eviction case against him dismissed earlier this year in February.

Ahern says that the fees are an example of an industry taking advantage of a population who is sometimes scared or unable to speak up.

“It is because people living there are considered or regarded as vulnerable and unable to fight the fees,” he said.