NEW YORK--33 women are taking part in a class-action lawsuit that alleges gender discrimination at MSLGroup.

The development comes after a US district judge ruled that current and former VPs and SVPs can join the case, which was filed last year by Monique da Silva Moore and four other plaintiffs.

Consequently, notices were sent to more than 100 current and former female employees from MSLGroup. It is understood that a further 28 women have now joined the suit, including two who are currently working for the firm.

The plaintiffs, who are seeking $100m, allege women were frequently overlooked for promotions and were not given the pay they were due.

In a statement released today, MSLGroup said: "We remain confident that the Moore lawsuit has no merit, and we believe that the relative lack of interest among the vast majority of those eligible to participate demonstrates the weakness of the claims.  We will continue to defend ourselves vigorously against these baseless claims, as we have done in the nearly two years since the lawsuit was filed."

The plaintiffs claim that 70 percent of MSLGroup parent company Publicis' 45,000 PR executives worldwide are women, but females occupy only 15 percent of the "leadership" positions.

Court documents from earlier this year also detail allegations of inappropriate behaviour by executives at the firm, including former MSLGroup Americas president Jim Tskonaos, who departed the firm in August.