Mark Peters, a Boston attorney, is threatening to take the issue to state officials. The authority, he contends, has committed “evident violations of the Open Meeting Law.”

A Jan. 28 letter sent by Peters to the authority on behalf of the residents’ group says that the author­ity has been “engaged for many months now in the conceptualization of and planning for the ‘development’ of the Newburyport waterfront . . . with almost no public discussion or disclosure of the options, opportunities, possibilities, and criteria that it must have considered.”

Peters closed the three-page missive by stating: “The Committee for an Open Waterfront Inc. makes demand by this letter that the authority desist from its secret deliberations. . . . If the authority ­declines to do so, the committee will bring the matter to the atten­tion of the attorney general of the Commonwealth and will request her intervention and investigation.”

Under the Open Meeting Law, when a governmental body discusses the public’s business, it must give ­advanced notice of meetings; hold its meetings in open session; and keep minutes of the meetings and make them public.

Reached at her Rowley home, Carol L. Powers, the attor­ney who has represented the authority since 1991, said, “There have been no violations of the Open Meeting Law.”

“In the Open Meeting Law, the term deliberations has a very specific meaning,” Powers said. “Deliberations mean decisions being made by the entire board. No deliberations, no ­decisions, have been made by the board outside of a public meeting at all.”

The authority has been holding open discussions concerning its waterfront property for nearly a year, but members of the Committee for an Open ­Waterfront say that members of the authority also discuss plans behind closed doors.

The Peters letter cited an inci­dent that he said occurred Jan. 16, when, immediately following the meeting the authority held on that date, “one or ­another of its members acknowledged that much of the authority’s planning for the water­front is being conducted ‘behind the scenes.’ ”

Peters said James Shanley, a former city councilor then serving as chairman of the author­ity, told the small group that lingered at the close of the authority’s meeting that the public was not welcome at the authority’s planning sessions “because members of the authority ‘can talk more freely when the public is not pre­sent.’ ”

Shanley, who stepped down as chairman of the authority last week, declined to discuss the issue and referred questions to Powers.

Shanley’s successor, Tom ­Salemi, who was named to the five-member board last year, said he was “at the [Jan. 16] meeting, but left immediately after it ended.”

Salemi, a professional writer and former community reporter, said he is committed to “keeping people informed” about the authority’s plans “to expand the park and connect the waterfront to the downtown.”

The authority is proposing to incorporate commercial and residential development on the property, now occupied by dirt and gravel parking lots. Under a proposal created by Union ­Studio, a Providence architectural firm hired by the authority, the land would become home to more green space and two mixed-use buildings, while maintaining up to 70 percent of the existing parking spaces.

Ultimately, the goal is “to draw people to the waterfront, not only in summertime when the weather is lovely, but in winter when people might want to sit in a coffee shop and watch the river,” Salemi said.

The authority’s property straddles Market Landing Park, with about 2.1 acres on each side. Under the Union Studio design, the buildings on the site would be subject to height restric­tions of about 35 feet and be placed close to the street to preserve as much open space as possible along the waterfront. The buildings would house coffee shops, restaurants, and ­retail shops on the ground floors with residential units on the upper floors.