Citing attorney-client privilege, a quasi-public state authority is refusing to disclose how much it is spending on legal fees fighting a $562,000 severance payment to an official who lost his job as a part of an authority consolidation last year.

Benson Caswell, the former executive director of the now-defunct Health and Educational Facilities Authority, is suing MassDevelopment, claiming the agency owes him a severance payment for terminating his employment after the two authorities merged. MassDevelopment claims the legislation merging the two authorities nullified the severance agreement.

The lawsuit, filed last October, has become a bitter contest of wills. In court filings, Caswell claims he is being denied his severance because he refused to appoint a political supporter of Gov. Deval Patrick to a top spot at HEFA. Officials in the Patrick administration says Caswell’s severance payment is a prime example of the sweetheart deals that were commonplace at state authorities before they began cleaning them up last year.

When the lawsuit was filed last year, the Boston Globe editorialized that Caswell’s severance arrangement should never have been approved but was nevertheless probably valid. “Patrick may not win a legal battle with Caswell, but it’s worth the fight,” the newspaper said.

To see if the fight is worth it, CommonWealth asked MassDevelopment how much it was paying the private law firm of McCarter & English LLP to represent it in the severance battle. MassDevelopment refused, claiming that payments to the firm’s attorneys represent privileged communication not subject to the state’s Public Records Law.

“MassDevelopment would be pleased to disclose how much it has spent on legal fees after the completion of litigation, but considers this information privileged at this time,” said spokesman Mark Sternman in an email to CommonWealth.

Sternman said the agency was relying on a 2007 Supreme Judicial Court decision that stated unequivocally that attorney-client communications are exempt from the Public Records Law. But that decision refers only to communications and advice provided by attorneys to their clients, not fees the clients pay to their attorneys.

MassDevelopment’s chances of winning the lawsuit are slim. Court records indicate Caswell’s severance agreement was properly negotiated with the former HEFA board and remained in force at the time the legislation authorizing MassDevelopment to absorb HEFA was approved. That legislation specified that all existing contracts at HEFA would remain in effect after the transfer to MassDevelopment.

Superior Court Judge Peter Lauriat recently rejected a bid by MassDevelopment to throw out most of Caswell’s claims, holding that Caswell has “set forth sufficient facts, at this early stage of the proceedings, to support an entitlement to relief.”