The state’s correction officers union is urging Gov. Maura Healey to slam the brakes on the closure of MCI-Concord, warning that this move would be dangerous and put “officers and inmates at risk.”

The Healey administration this week said MCI-Concord, the oldest men’s prison in the Bay State, will shut down by the summer — and that the inmates and officers will be transferred to other facilities.

MCI-Concord, a medium-security men’s prison, currently operates at 50% capacity and has an incarcerated population of about 300 inmates. State officials touted this closure as a cost-saving move amid the state’s lowest prison population in 35 years.

On Thursday, the Massachusetts Correction Officers Federated Union addressed a letter to Healey, as the union pushed the governor to halt the prison closure.

“The MA Correction Officers Federated Union is deeply troubled about the closing of MCI Concord,” the union’s legislative representative Kevin Flanagan wrote in the letter, later adding, “With the planned closing we are concerned over how this will happen logistically and how it will place our other facilities at an increased threat level.”

MCI-Concord closing would be the fourth prison shutdown in three years, the legislative representative noted.

“And that stretches the system too thin, with no viable plan to house these most dangerous inmates,” he added. “This would force higher security inmates to co-mingle with lesser security inmates and place them at risk.”

Flanagan said that when Walpole closed, many of the inmates from there got transferred to Souza-Baranowski Correctional Center. Since then, there has been a “tremendous increase” in assaults on staff and inmates, the union reported.

In a six-week period, more than 40 assaults on officers were reported, and more than 600 disciplinary reports were recorded.

“With Concord closing we are concerned that inmates there and at other facilities will be re-classified to lower security facilities,” Flanagan wrote. “When this happens, it puts officers and inmates at risk.”

“We are asking you and your administration to stop the closing of Concord and study the impact this will have in our correctional system,” the legislative representative later added. “MCOFU would like to be fully involved in the classification process of inmates. This will ensure that inmates with violent or disruptive behavior not be classified to lower security facilities just to make space.”

Closing MCI-Concord will save about $16 million in annual operating costs, along with $190 million in overall upkeep costs.

“Commissioner Mici and the DOC leadership team are deeply committed to working closely with employees and their union representatives to address any safety concerns and to ensure a fair and equitable relocation of all affected staff to other facilities,” a DOC spokesperson said in a statement on Thursday.

“We are grateful to our corrections staff for their hard work and service,” the spokesperson added. “As we continue to shape the future of our agency, we are confident that together we can take this essential step to eliminate redundancies, enhance efficiency and ensure a more effective and impactful correctional system while still ensuring the safety of our staff and incarcerated individuals.”