Mayor Wu has put Carney Hospital’s landlord on notice: She wants the hospital site to continue to be used for health care and plans to block any attempt to “capitalize on the closure of Carney Hospital by redeveloping the property.”

In a letter sent on Thursday, Wu warned Edward Aldag, the chairman and CEO of Medical Properties Trust (MPT)— the company that owns the Carney campus on Dorchester Avenue— that she’ll make sure city planning boards shoot down any future efforts to demolish the hospital buildings and replace it with housing or any other re-use.

“I would like to be absolutely clear that my Administration will oppose any effort by ownership to rezone the property for uses other than the provision of health care.”

Wu’s letter notes that the Carney site at 2100 Dorchester Ave. is currently zoned as Multi-Family Residential, which allows for residential housing, but only a specific type up to “3 stories or 35 feet”— roughly the size of a traditional Dorchester three-decker. “This zoning supports maintaining the site as a hospital/health care facility due to how difficult to would be to accomplish a financially feasible alternative use that is compliant with the existing zoning,” Wu writes, later adding: “Any chance to zoning would require review by multiple boards and commissions and my Administration will oppose any efforts by your representatives to secure one.”

Wu’s admonition comes just a few days after she appeared at a rally alongside other political leaders in which she signalled support for Carney’s cause and pledged to work closely with stakeholders to “figure out away together.”

But Wu’s letter marks a new front in the city’s public campaign to save Carney from closure or, at least, find a path towards operating it as a health care facility again in the near future. Steward Health Care, which operates Carney, plans to shutter Carney on Aug. 31 under a court-supervised proposal that it made public last week in a US bankruptcy court proceeding in Houston, TX. Steward also plans to close a second Massachusetts hospital, Nashoba Valley Medical Center in Ayer, Mass.

Steward claims that it received no “actionable” offers to acquire Carney during a recent auction process which has been hidden from the public’s view. However, that claim has been disputed by the Massachusetts Nurses Association and other sources, who say that at least one bid was on the table for Carney. In a letter filed with the court this week by Attorney General Andrea Campbell, her office alleged that MPT and Steward “are trying to block possible transactions to transition Steward’s Massachusetts Hospitals to new operators to extract concessions from the Steward estate and their mortgagee.”

Supporters of keeping the Carney and Nashoba open have urged Gov. Maura Healey and her senior staff to reject the current Steward plan and their attempt to close the facilities with just one month’s notice. After initially suggesting there was nothing she could do about the closures, Healey has since taken a tougher stance, telling reporters on Thursday that she intends to press Steward to adhere to a state policy that requires 120-days notice before any attempted closure.

Wu’s letter to the MPT chairman and a second executive— Karl Kuchel of Macquarie Infrastructure Partners— is seen as an important lever needed to convince Steward and its various creditors to make a course correction in the case of Carney specifically.

Sources familiar with the tightly-held bidding process say Carney’s nearly 12-acre campus property has been deemed more profitable to sell-off as a redevelopment opportunity to benefit the various parties to Steward’s bankruptcy case. The city of Boston currently lists the property’s assessed value at $76 million, according tax records, although the market-rate value is likely significantly higher.

In her two-page letter, Wu reminds the two executives that her office “has committed to cooperate fully in any state and federal investigation of illegal conduct by you and other entities involved in Steward’s collapse.”

“We will also hold you to your financial and maintenance obligations as large property owners. In the meantime, we wish to clearly communicate that, as to the hospital property, my Administration is opposed to any proposals that would allow you to take further advantage of this community.”