NEW YORK—A federal judge has granted conditional class action certification to a gender discrimination lawsuit filed by current and former female public relations professionals of a major French advertising company and one of its units.

In a ruling issued Friday, U.S. District Court Judge Andrew L. Carter Jr. also approved sending notices to potential opt-in plaintiffs in the lawsuit filed against Paris-based Publicis Groupe S.A. and its MSLGroup unit.

The conditional certification means that additional discovery must be conducted. The ruling applies only to MSLGroup's U.S. operations, which are based in New York. The lawsuit originally was filed in April 2011 by New York-based law firm Sanford Wittels & Heisler L.L.P.

The potential class is about 125 female employees, according to the decision.

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In his ruling, Judge Carter said the court concludes that “plaintiffs have met their burden by making a modest factual showing to demonstrate that they and potential plaintiffs together were victims of a common policy or plan that violated the law. They submit sufficient information that because of a common pay scale, they were paid wages lower than the wages paid to men for the performance of substantially equal work.”

Sanford Wittels Partner Janette Wipper said she was delighted by the judge’s ruling “because it will provide female Publicis Groupe professionals an opportunity to participate directly in this suit. And even more importantly, it brings women one step closer to making equal pay for equal work a reality in the PR industry,” she said in a statement.

MSLGroup said in a statement, in part, that the ruling “was a procedural ruling only and not unexpected. It does not resolve the merits of the claims.”

“The court made no decision as to whether the case may proceed as a class action, and it will not decide that issue until sometime next year,” according to the statement. “Additionally, the court made no finding that our pay practices are discriminatory; any final decision on this issue will not be made until the trial, which we expect to occur sometime in 2014.”