NEW YORK (Reuters) - Bank of America Corp and Royal Bank of Scotland Group Plc have been sued by investors in the United States over their alleged roles in a conspiracy among eight banks to rig prices in the $9.4 trillion European government bond market.

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The proposed class-action complaint accusing the banks of violating federal antitrust law was filed on Monday night in U.S. District Court in New Haven, Connecticut.

It followed a Jan. 31 announcement by the European Union’s antitrust authority accusing the eight banks of being part of a cartel to distort bond prices from 2007 to 2012.

In a “Statement of Objections,” the European Commission said it believed bond traders may have illegally shared commercially sensitive information and coordinated trading strategies, mainly through online chatrooms.

While the commission did not identify the eight banks, media reports said Bank of America and RBS are among them.

Bank of America spokesman Bill Halldin declined to comment on Tuesday. RBS also declined to comment.

According to the complaint, banks profited at investors’ expense by conspiring to widen the bid-asked spreads they quoted, thereby increasing the prices that investors paid for bonds and decreasing the prices at which they sold bonds.

The banks’ tactics were “strikingly similar” to those used in the foreign exchange market, the complaint said, where banks paid more than $10 billion in fines to settle enforcement claims in several countries. Several banks also entered guilty pleas.

Suspected cartel members that have yet to be publicly named were identified as “John Doe” defendants in the complaint.

A lawyer for the plaintiffs did not immediately respond on Tuesday to requests for comment. The plaintiffs are led by the Electrical Workers Pension Fund Local 103 I.B.E.W. in Boston.

U.S. courts are home to a wide array of private litigation accusing banks of conspiring to rig various financial markets, interest rate benchmarks and commodities.

The case is Electrical Workers Pension Fund Local 103 I.B.E.W. et al v Bank of America NA et al, U.S. District Court, District of Connecticut, No. 19-00314.