Constance R. Caplan, chair of the Hirshhorn Museum and Sculpture Garden, has tendered her resignation. She complains of "shocking breaches of confidentiality, inappropriate interruptions during Board meetings, and other negative behavior" at the museum in a letter published by the Washington Post.

Caplan indicated in a phone conversation with A.i.A. today that her resignation resulted from discord between the board and the institution's executive director.

"We're coming into times when I think that museum finances are going to become more difficult," Caplan said. "I believe that Congress is going to be tougher on institutions like the Smithsonian. They will have to be able to generate increased private support, which makes a board role even more important. There has to be a healthy partnership between the board and the executive director."

The Washington, D.C., museum, which is part of the Smithsonian Institution, saw the departure of its director, Richard Koshalek, last month. He had been in the post since April 2009. His resignation was originally to be effective at the end of the year, but a call to the museum today revealed that he left at the end of June.

The Washington City Paper cites unnamed sources who indicated Koshalek resigned "because he didn't believe he had support for his vision for the Hirshhorn." Six other board members have resigned since 2012. Caplan was chair since October 2012, when the previous chair, J. Tomilson Hill, resigned from the post.

Caplan further states in her letter that "the full Hirshhorn Board was not given the opportunity by the Smithsonian to carefully review and be apprised of the appointment of the interim Director in advance—a routine courtesy at other leading institutions." Kerry Brougher, deputy director and chief curator of the museum, will serve as acting director, the museum announced in June.

She goes on to complain that she was not consulted in "setting agendas, meeting dates and Trustee activities of the Board."

Caplan is the chair of The Time Group/Washington Place Management, a Baltimore, Md., real estate and management company. She also serves as a trustee emeritus at Johns Hopkins University and on the board of organizations including the Baltimore Symphony and, from 1995 to 2010, of New York's DIA Foundation.

Neither the Smithsonian nor the Hirshhorn responded immediately to requests for comment.