A federal judge has approved JPMorgan Chase & Co.’s $150 million settlement of a lawsuit by the American Federation of Television and Radio Artists retirement fund and other investors over losses that the plan sustained from the bank’s Sigma Finance hedge fund.

U.S. District Court Judge Shira A. Scheindlin filed the settlement on Wednesday. The bank said on its website that the filing commenced a 30-day appeal period and that if no appeals are filed, the settlement will become effective.

The bank and the AFTRA fund had no comment.

The settlement with investors was disclosed in March. The AFTRA fund and the bank announced on Feb. 7 that they had reached a tentative settlement.

The suit alleged that JPMorgan Chase lost a “substantial portion” in cash collateral in medium-term notes issued by Sigma Finance Inc., a structured investment vehicle sponsored by Sigma Finance Corp. It said creditors seized over $25 billion of Sigma’s $27 billion in assets in September and October 2008, leaving about $1.9 billion as security for about $6.2 billion of outstanding medium-term notes.

Sigma once carried “triple-A” ratings, but the suit alleged that JPMorgan “buried its head in the sand and refused to heed the warning signs” when analysts predicted in 2007 that Sigma would be unable to repay the notes.

Other plaintiffs in the JPMorgan case are the Manhattan and Bronx Surface Transit Operating Authority Pension Fund in New York City, and the Imperial County Employees’ Retirement System in El Centro, Calif.

Athough AFTRA merged with the Screen Actors Guild on March 30, the unions’ respective health and retirement plans remained intact and were not combined.