The plaintiffs accuse Sanofi-Aventis US management of sex discrimination, saying they were not promoted because of their gender and were paid significantly less than their male colleagues.
The women are seeking more than 300 million dollars in compensation.
Sanofi-Aventis denied the allegations.
The original plaintiff, Bellifemine, started working at Sanofi-Aventis US in 1995 and is still employed there. The three others -- Amy Zeoli, Michelle Popa and Sue Sullivan -- said they resigned in 2006-2007 over the situation.
All four plaintiffs said their bosses had sexually harassed them, in words or unwelcome gestures. Some said they suffered repeated incidences of harassment after reporting the offensive behavior to management.
"We'll be moving for class certification on behalf of approximately 6,000 women in the next few months, after we obtain the statistical data which shows that Sanofi pays its female pharma reps less than men, and fails to promote women at the same rate as men," said a lawyer for the plaintiffs, Steven Wittels of Sanford Wittels & Heisler LLP.
"We are confident that the data will support these claims," he said.
Wittels said the 300 million dollars sought was modest because "each woman is entitled to up to approximately 500,000 dollars in damages for compensatory back and future wages and punitive damages."
Sanofi-Aventis US issued a terse statement denying the women's allegations.
"We are confident that the suit lacks merit and that all of our employees are treated fairly and in compliance with all applicable federal and state laws," the company said.
