Did this environmental group cross the line? Or does an overdeveloped waterfront need defending?

For Bradley Campbell, waterfront access is key. Above, the proposed 150 Seaport.Elkus Manfredi

On the booming Boston waterfront, Bradley Campbell was very much a new face on the docks.

A veteran of environmental protection work in Washington, D.C., and New Jersey, he arrived in the city in late 2015 as the new president of the Conservation Law Foundation, a venerable environmental advocacy group perhaps best known for its 1980s court fight to clean up Boston Harbor. One of his top priorities: Defend the public’s access to the waterfront amid a surge in development.

Over more than 50 years, the foundation had earned a reputation as a responsible advocate, even when it resorted to litigation to achieve its goals. But in several recent showdowns, Campbell has riled Mayor Martin J. Walsh, other city officials, and community groups with what they say is a combative and arrogant approach that threatens to erode the organization’s effectiveness.

The source of the tension centers on the foundation’s challenge to 150 Seaport, a high-profile tower planned by developer Jon Cronin on the South Boston site of his Whiskey Priest and Atlantic Beer Garden bars.

In one meeting about the project, Campbell was said to be so dismissive that a community member questioned whether he was trying to negotiate or to kill the development outright.

Walsh, frustrated with Campbell’s behavior in another session last fall, walked out of his City Hall office.

And former state senator Linda Dorcena Forry lashed out at him at a State House meeting for persisting in his fight against the project, even though it had widespread government and neighborhood support.

In a two-page letter to the CLF’s board of trustees in January, Walsh described the September meeting with Campbell as “an effort to reach a consensus about [the foundation’s] outstanding concerns” about 150 Seaport.

“We were met by Mr. Campbell with disrespectful, contemptuous, and combative language, and a suggestion that my staff and I were not capable of negotiating appropriate outcomes for the people of Boston and that it was his job to do it,” the mayor wrote.

Separately from the Cronin project, one top city official accused Campbell of possibly unethical behavior in an inter-departmental memo obtained by the Globe, for allegedly advocating on behalf of a Boston developer, Don Law, who is married to the chair of the foundation’s board, Sara Molyneaux.

“I’m asking you and your team to be super-vigilant in any dealings with [the foundation],” Brian Golden, head of the Boston Planning & Development Agency, wrote in a memo to staff after meeting with Campbell last year, accusing him of “inappropriate” behavior and saying he was crossing ethical lines or “coming dangerously close.”

“We need to be cautious with them and, perhaps, affirmatively call out [the foundation] when we believe they are making — from a legal or ethical perspective — an inappropriate ask,” Golden wrote in the memo.

In an interview, Campbell strongly denied that he had ever advocated for Law, saying he would not give preference to any developer. He said Molyneaux recuses herself from any Conservation Law Foundation discussions involving her husband’s projects.

In the case cited in Golden’s memo, Campbell acknowledged that he both questioned the status of a city development designation for a coveted parcel in Marina Park and suggested he may challenge it. But he denied advocating for Law to get development rights over the site.

Campbell also defended his organization’s strategy for advocacy, saying the foundation is acting in the public interest to monitor a waterfront that it helped clean up. Campbell said that public officials oppose the intervention because the group is challenging what he described as the city’s failure to hold developers more accountable.

“We have fought for 50 years to protect public access on the waterfront,” said Campbell, who has worked in the private sector and at the US Environmental Protection Agency, and headed New Jersey’s Department of Environmental Protection. “Our foremost concern is to protect the public realm.”

But community and public officials say Campbell has set the organization on a collision course with city planners.

In his January letter, Walsh complained that the group and Campbell’s tactics could jeopardize the city’s development efforts by alienating builders.

“The methods employed by [Campbell] are neither good for [the foundation] nor the people of Boston,” the mayor said.

The head of the Gavin Foundation in South Boston, which provides substance abuse recovery services and supported 150 Seaport, wrote separately to Molyneaux in January, saying that Campbell’s behavior at community meetings “is putting the reputation of the Conservation Law Foundation at risk.”

“A new perspective is needed,” John McGahan, president of the Gavin Foundation, said in the letter, calling Campbell “offensive and rude.”

Campbell, 57, isn’t backing off. The foundation recently threatened to file a lawsuit challenging state approval earlier this month of a Downtown Waterfront Municipal Harbor Plan that could enable two other major tower developments there.

The CLF’s waterfront campaign is funded in large part by donations and grants, including significant support from the Barr Foundation, which has donated at least $630,000 since late 2015 for a “multiyear waterfront campaign.”

James E. Canales, president and a trustee of the Barr Foundation, said his organization chose to support the Conservation Law Foundation as a partner in its own campaign to improve public access to the waterfront based on its history of advocacy and specialty in state law that governs waterfront activity.

Canales said he was not involved in the Conservation Law Foundation’s day-to-day activities or all of its interactions with public officials, so he could not comment on them, though he said he found Campbell to be “collegial, to be constructive, and to be thoughtfully engaged” in meetings that he did attend.

He added that advocacy work is expected at times to turn “heated.”

“By its very nature, advocacy work is going to leave a difference of opinions,” he said.

Walsh isn’t the only one unhappy with Campbell’s handling of 150 Seaport.

“It felt like they were looking to pick a fight, they weren’t looking to compromise, and we couldn’t understand why,” said Donna Brown, executive director of the South Boston Neighborhood Development Corporation, who attended several community meetings with Campbell, including the one at Forry’s State House office. “They were combative. It was not a ‘let’s find a way to get to yes.’ ”

The project had already been approved at the city level, with widespread community support, but the foundation filed a lawsuit last year challenging the state’s review of the development under the Massachusetts Public Waterfront Act.

The foundation offered to settle the lawsuit, according to interviews with people familiar with the negotiations and documents reviewed by the Globe, in exchange for $40 million in funding for a future, unidentified park. Lawyers for the developer, Cronin Holdings, and others familiar with the negotiations saw that as an outlandish request, a pretext to engage the developer in costly litigation or force it to abandon the project.

The foundation and the developer ultimately settled for $13 million to fund a nearby park. The agreement was reached earlier this year, a week after the Globe began inquiring about the negotiations.

Campbell said at the time that the $40 million demand was based on an assessment of the value of the land and permits the city had granted for the project, and that the foundation intends to use that formula for negotiating with other developers in the neighborhood.

“We got a lot of pushback from the city because their paramount interest is shovels in the ground,” Campbell said. “We’re not interested in blocking things. We’re interested in making sure the public gets its due.”