(Reuters) - A U.S. judge must redefine which groups of investors can sue Brazilian state-controlled oil firm Petroleo Brasileiro SA in their bid to recoup billions of dollars of alleged losses tied to its corruption scandal, a U.S. appeals court said on Friday.

The logo of Petrobras, state-controlled Petroleo Brasileiro SA, is seen at President Bernardes Refinery in Cubatao, Brazil June 8, 2017. REUTERS/Paulo Whitaker

But the 2nd U.S. Circuit Court of Appeals in Manhattan also rejected Petrobras’ request that it impose a tougher standard for investors to meet before showing they were defrauded.

Jeremy Lieberman, a lawyer for the investors, in a statement said he was “very pleased” with the decision, and that it cleared the way for his clients to seek a trial date. The litigation had been put on hold pending resolution of the appeal.

Petrobras had no immediate comment on the ruling.

Investors sued after prosecutors in Brazil accused former Petrobras executives of accepting more than $2 billion in bribes over a decade, mainly from construction and engineering companies.

Petrobras claimed it was itself a victim, but its market value plunged as the scandal deepened.

In February 2016, U.S. District Judge Jed Rakoff in Manhattan said two classes of plaintiffs could pursue their claims together, potentially allowing for higher recoveries.

One class included purchasers of Petrobras securities from January 2010 to July 2015, led by Universities Superannuation Scheme of Liverpool, England.

The other included purchasers of debt securities from offerings in 2013 and 2014, led by North Carolina’s treasurer and the Employees’ Retirement System of Hawaii.

Lawyers for Petrobras countered that it was unclear whether the investors were conducting the relevant transactions in the United States, which was necessary for certification.

They also said the plaintiffs had failed to adequately show that news of the bribery and political kickback scandal in Brazil dragged down Petrobras’ stock price.

In Friday’s decision, the appeals court said Rakoff had not come up with broad enough criteria to define the classes.

“On remand, the district court might properly certify one or more classes that capture some or all of the securities holders who fall within the classes as currently defined,” Judge Nicholas Garaufis, who normally sits on the federal district court in Brooklyn, New York, wrote for the appeals court.

The court upheld Rakoff’s finding that the investors deserved a “fraud on the market” presumption, that all public information about Petrobras was reflected in its stock price.

This meant investors need not show they relied on specific misrepresentations when buying Petrobras securities, but only that they bought before the truth became known.

The case is In re: Petrobras Securities Litigation, 2nd U.S. Circuit Court of Appeals, No. 16-1914.