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“For decades, corporations misled us about their massive impact on climate change,” Liss-Riordan says in the ad. “In Massachusetts, we’ve passed good laws to hold big polluters accountable. But laws don’t enforce themselves.”

She promised to stand up to corporate polluters and “lead the national fight against climate change.”

In their letter, eight environmental advocates — including George Bachrach, the former president of the Environmental League of Massachusetts, and John DeVillars, a former regional administrator of the Environmental Protection Agency — accused Liss-Riordan of inflating her environmental record.

“You were not with us when we fought for the ‘good laws to hold polluters accountable,’” they wrote. “You were not with [Attorney General] Maura Healey and other litigators in court holding polluters like ExxonMobil accountable.”

They added: “Over more than two decades we never once saw you at the court house or the State House … Yet you run this TV ad claiming your twenty years as a private litigator demonstrates leadership on the environment … when you were needed in the court house or at the State House, you were missing in action.”

Kevin Ready, a spokesman for Liss-Riordan, called the allegations against her a “politically motivated attack” and accused the advocates of doing dirty work for her opponents, particularly former Boston city councilor Andrea Campbell.

“As this race gets closer and Shannon moves up in the polls, we expect to see more desperate ploys like this from our opponents,” Ready said.

Campbell has led the race for months, buoyed by name recognition from her candidacy in last year’s mayoral campaign in Boston. But Liss-Riordan, who has spent significant amounts of her own money on TV ads and direct mail this summer, has surged in the polls.

MassINC Polling Group recently found Campbell leading the race with 28 percent of those polled. But Liss-Riordan trailed by just 2 points, well within the poll’s margin of error. Quentin Palfrey, who ran for lieutenant governor in 2018 and is also now in the race for attorney general, had 10 percent.

Ready noted the ad was no longer airing on TV, though it remains online.

“These antics should not distract from the fact that one candidate in this race, Andrea Campbell, continues to accept money from fossil fuel industry lobbyists, despite pledging not to,” Ready said.

In June, Liss-Riordan accused Campbell of accepting campaign contributions from a lobbyist for ExxonMobil.

Campbell’s campaign declined to comment on that Friday.

In a statement, Palfrey said: “I am proud of our campaign’s plan to inject urgency into the fight against climate change,” noting he was endorsed by the environmental groups 350 Mass and the Massachusetts chapter of the Sierra Club.

During a candidates’ debate this month, Liss-Riordan called Campbell’s donor list “a who’s who of lobbyists for fossil fuel industries (and) the Koch brothers,” according to the State House News Service. Palfrey alleged Campbell “received $2 million in super PAC support in last year’s mayor’s race.”

During the debate, Campbell responded by saying Palfrey was relying on public matching funds and Liss-Riordan was financing her campaign with some $3 million of her own money.

“I’ve always been accountable to the people,” she said, according to the State House News Service. “I will remain accountable to the people.”

Ready described Liss-Riordan as “by far the most qualified candidate for attorney general to use the law to take on those who are destroying our environment and contributing to climate change.” He noted that she has also proposed setting up a “Green Bank” to help finance environmental justice projects.

In response to the allegations, he noted that Campbell was being supported by the Environmental League of Massachusetts Action Fund.

Bachrach, who retired from the Environmental League of Massachusetts, said he has no connection to the Campbell campaign.

“While I left ELM five years ago, the endorsement of Campbell by environmental groups is based on her record,” he said.

In their letter, the environmental advocates accused Liss-Riordan of seeking labor endorsements from “those eager to build gas pipelines that will prolong our dependence on fossil fuels.”

“It is cynical, deceiving, and offensive to those of us (and thousands of others) who were in the climate trenches, for you to take any credit on the environment,” they wrote.

The letter was also signed by Kelsey Wirth, cofounder of Mothers Out Front; Jack Clarke, former legislative director for Mass Audubon; Bob Massie, who has led several environmental groups and was a former candidate for governor; as well as longtime environmental advocates Sonia Hamel, Christina Pacheco, and Thaleia Schlesinger.