The federal agency that monitors workplace dangers has issued a $207,000 fine against a private psychiatric hospital in Lowell for failing to protect its workers from violent patients.

The Occupational Safety and Health Administration said that Lowell Treatment Center promised more than a year ago to fix a range of safety violations.

But since last December, violent patients have badly beaten at least three workers at the 41-bed hospital, causing black eyes, bruises, one concussion and weeks lost from work, according to OSHA documents.

The Lowell facility is owned by the for-profit Universal Health Services, the country’s biggest provider of mental health care. The publicly traded company is based in King of Prussia, Pa., and operates in Massachusetts as Arbour Health System.

The company has frequently come under fire from state and federal regulators for patient-care violations and concerns over the physical safety of its workers.

In June, OSHA notified the company that its employees still faced serious hazards at the Lowell site.

Employees working at the treatment center in Lowell “were exposed to acts of workplace violence, including … verbal threats of assault, assaults, choking, punching, kicks, bites, scratches and/or pulling of hair,” OSHA official Anthony Covello wrote.

Judy Merel, a spokeswoman for Arbour Health System, disputed the charges from OSHA, saying that the company is meeting or exceeding worker safety guidelines.

In an email, Merel called OSHA’s statement “inaccurate” and said Lowell Treatment Center is “committed to the safety and well-being of our patients, their families and our staff.”

Social worker David Wilensky worked at the Lowell Treatment Center for 11 years, but quit last year partly out of concern for employee safety.

"The staff turnover on the inpatient units was very high, and they had a hard time keeping people employed there because people got hurt,” Wilensky said. “I had several friends taken out on stretchers at one time or another.”

State legislators are debating a range of bills aimed at preventing the violence faced by hospital workers. Karen Coughlin, a member of the Massachusetts Nurses Association, said the problem is getting worse.

“Between 2012 and 2014, the incidence of violence nearly doubled for nurses and nurse assistants,” said Coughlin.

OSHA’s most recent enforcement at the Lowell Treatment Center comes amidst increased oversight of Arbour-owned hospitals by numerous regulators, including the Massachusetts Department of Mental Health, which licenses the hospital, the Centers for Medicare and Medicaid Services and the U.S. Department of Justice.

Two years ago OSHA issued a “hazard alert” letter issued to Pembroke Hospital, which is also owned by Arbour, that flagged the high number of workers assaulted by violent patients and called for improved staffing and safety measures.

OSHA opened an earlier investigation into Pembroke Hospital after a 22-year-old patient attacked a nurse and nearly tore off her ear when she was trying to place him in restraints. OSHA has said it has found no violations in that probe.