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Manhattan Institute one of eight conservative advocacy groups that filed amicus briefs urging the court to hear Moore v US

An influential thinktank closely linked to two billionaires who provided lavish travel gifts to conservative supreme court justices is behind a successful lobbying campaign to get the US high court to take on a case that could protect them and other billionaires from a possible future wealth tax.

The Manhattan Institute was one of eight conservative advocacy groups that filed amicus briefs urging the supreme court to take on Moore v US, a $15,000 tax case that Democrats have warned could permanently “lock in” the right of billionaires to opt out of paying fair taxes.

Billionaire hedge fund manager Paul Singer is chairman of the Manhattan Institute and Kathy Crow, who is married to real estate mogul Harlan Crow, serves as a trustee of the group. Both have provided two of the justices – Samuel Alito and Clarence Thomas, respectively – with private travel gifts and have socialised with the judges on lavish vacations, according to reports in ProPublica and other media outlets.

The revelations have stoked serious accusations of ethical and legal violations by the two rightwing justices, who failed to disclose the travel and – in Thomas’s case – hundreds of thousands of dollars in additional gifts from the Crows, including property purchases and private tuition payments for Thomas’s grand nephew.