Lawyers for the women are seeking class-action status and say the class could include thousands of women. The suit was filed in May, when it specified that damages sought would exceed $1 million.
"We are confident that this case lacks merit, and the company will vigorously defend itself," a company spokeswoman said in a statement, adding that New Jersey-based Merck provides parental leave with job protection, flexible work arrangements, and on-site child care at some locations.
The lawsuit says Merck managers told female sales representatives who had been well-regarded that they were given negative reviews "because they were pregnant or had taken leave."
Women representatives were also referred to as "whores," the suit says.
One plaintiff said she was laid off while on medical leave due to pregnancy-related health problems. The company urged her to apply for other jobs while on leave, and she applied for them as she was checking into the hospital for Caesarean-section surgery, the suit says.
Two of the five plaintiffs lived or worked locally - Kelli Smith in Merck's Toms River, N.J., office, and Kandice Bross in Merck's Wilmington office. Smith left in December, the suit says, after learning that promotion prospects were dim.
The lawsuit says the company's human resources department ignored complaints or allowed managers to retaliate against women who made them, a charge the company denies.
Sanford Heisler L.L.P., the New York law firm representing the women, won a $253 million jury verdict in a gender discrimination employment case against Novartis Pharmaceuticals Corp. in 2010. Merck is being represented by Morgan, Lewis & Bockius L.L.P. in Philadelphia.