A civil rights group issued a call Saturday for US supreme court justice Samuel Alito to be investigated over allegations that the judge leaked a 2014 landmark ruling involving contraception and religious rights at a private dinner with wealthy political donors.

The claim was contained in a New York Times article in which minister Rob Schenck, an anti-abortion activist, said he was told of the decision weeks before it was announced and had used the information to prepare a public relations push.

Schenck also claimed he tipped off Hobby Lobby, the craft store chain owned by Christian evangelicals that brought and won the case allowing privately-held, for-profit businesses to be exempt from regulations to which its owners religiously object, in this case requiring employers to cover certain contraceptives for their female employees.

“The Senate judiciary committee should immediately move to investigate the apparent leak by Justice Alito,” said Brian Fallon, the executive director of Demand Justice.

“This bombshell report is the latest proof that the Republican justices on the court are little more than politicians in robes. It’s no wonder trust in the court has hit a record low. Structural reform of the court, including strict new ethics rules, is needed now more than ever.”

Fallon added that Schenck “should be called to testify about both the leak and the years-long lobbying effort he once led to cultivate Alito and other Republican justices”.

Claims of the judicial leak, potentially for political purposes, comes six months after a draft opinion of the Dobbs decision overturning the nationwide abortion rights established by the 1972 case Roe v Wade was leaked ahead of its June publication.

In a letter to supreme court chief justice John G Roberts Jr dated 7 June, Schenck wrote that he was reaching out to the judge “to inform you of a series of events that may impinge on the investigation you and your delegates are undertaking in connection with the leak of a draft opinion”.

He described a dinner at which an unnamed political donor invited to dine at the home of Alito and his wife, Martha-Ann, had offered to try to glean information about the pending decision in the Hobby Lobby case.

The next day, the Times reported, the dining guest called Schenck and told him Alito had written the majority opinion in the case and that Hobby Lobby would win. That exact decision was publicly announced less than a month later.

Schenck concluded the letter to Roberts by saying he “thought this previous incident might bear some consideration by you and others involved in the process”.

How that directly reflects on the current investigation into the leak of the Dobbs decision is not clear, but it arrives at a time of concern for the court’s legitimacy as it works under the sway of a conservative supermajority. Polls show that a majority of Americans are losing confidence in the supreme court.

After the leak in May of the Dobbs decision draft, Alito called the unauthorized disclosure “a grave betrayal” and ordered an investigation by the supreme court’s marshal.

The Times noted that Schenck’s account has “gaps”. But the newspaper’s examination of the claim uncovered emails and conversations that “strongly suggested” that Schenck knew of the decision before it was made public.