In a sour ending to a longtime relationship, the Miccosukee Indians have accused their former lawyer, Dexter Lehtinen, of committing malpractice when he advised the tribe on income-tax issues stemming from the distribution of hundreds of millions in gambling profits to members.

The tribe says in a lawsuit that it paid Lehtinen $50 million as general counsel over the past two decades, but that following his advice has landed the Miccosukees in a costly legal fight with the Internal Revenue Service.

The tribe, which is seeking class-action status in the suit filed in Miami-Dade Circuit Court Monday, asserts that Lehtinen’s “negligent misrepresentation” has exposed about 250 members to tax assessments, interest and penalties “in the millions of dollars.”

The potential class could grow: The West Miami-Dade tribe has about 600 members, including minors.

Lehtinen, a former U.S. attorney in South Florida whose wife is U.S. Rep. Ileana Ros-Lehtinen, R-Miami, told The Miami Herald there is “no basis” for the tribe’s malpractice suit.

“As the case proceeds against me, the public will see they have come after the wrong guy,” he said, adding that the exorbitant legal payments cited in the suit are “not true” either.

“They always told me they were a sovereign entity and they didn’t owe taxes to the federal government,” he said of his former clients. “I told them repeatedly for a decade that they have to pay their taxes, and they fired me when I gave them a detailed memo’’ on the topic last year.

Lehtinen, who cut a high profile while representing the tribe on environmental issues, was terminated in May 2010 by a new Miccosukee Tribal Council headed by Colley Billie, who replaced longtime chairman Billy Cypress. Cypress himself has been sued by the IRS for failing to report and pay millions of dollars in back taxes — a chronic problem over the past decade resulting from his gambling junkets and spending sprees around the country, court records show.

As a sovereign nation, the tribe as an entity is not subject to taxes, though individual members must pay taxes on income from the tribe or any other source, including distributions from Indian gaming operations, several legal experts say.

The Miccosukees have historically kept secret their gambling revenues and how they distribute profits to tribe members, including flouting a regulatory law that requires them to file a distribution plan with the U.S. Bureau of Indian Affairs.

The Miccosukees are the only tribe in the United States that doles out gambling profits to members but fails to follow the law under the Indian Gaming Regulatory Act, according to the bureau.

In 2005, the National Indian Gaming Commission issued a bulletin saying that tribes can make gambling distributions as long as they file a plan, report the income payments and withhold taxes.

Yet during recent high-stakes civil litigation over the Miccosukees’ financial records, the tribe accused the IRS of harassment, saying the agency had no legal basis for investigating them. In the end, the Miccosukees lost when U.S. District Judge Alan S. Gold ruled the U.S. government’s sovereign power trumped the tribe’s.

Gold ordered the tribe to turn over voluminous financial records to the IRS for a civil investigation into its alleged failure to report and withhold income taxes on casino profits distributed to hundreds of its members from 2006-2010.