The 19 senators planned to file a brief before the court, which is still weeks away from considering the closely watched case. Sen. Patty Murray, D-Wash., who planned to make her case on the Senate floor, adamantly defended the Obama administration's side.
"What's at stake in this case before the Supreme Court is whether a CEO's personal beliefs can trump a woman's right to access free or low-cost contraception under the Affordable Care Act," she said in prepared remarks.
But Republican senators returned fire, jumping to Hobby Lobby's defense in a brief of their own.
"The ability to practice the faith we choose is one of our great constitutional rights. The Obama administration's contraceptive mandate stomps on that right," Sen. David Vitter said in a statement. He joined Sens. Ted Cruz, R-Texas; John Cornyn, R-Texas; and Mike Lee, R-Utah in the brief.
The dueling arguments come as the Supreme Court prepares to consider the case. The justices said in November they would take up the issue, which has divided the lower courts in the face of roughly 40 lawsuits from for-profit companies asking to be spared from having to cover some or all forms of contraception.
The Obama administration promotes the law's provision of a range of preventive care, free of charge, as a key benefit of the health care overhaul. Contraception is included in the package of cost-free benefits, which opponents say is an attack on the religious freedom of employers.
The court will consider two cases. One involves Hobby Lobby Inc., an Oklahoma City-based arts and crafts chain with 13,000 full-time employees. Hobby Lobby won in the lower courts.
The other case is an appeal from Conestoga Wood Specialties Corp., a Pennsylvania company that employs 950 people in making wood cabinets. Lower courts rejected the company's claims.
The court said the cases will be combined for arguments, probably in late March. A decision should come by late June.
The cases center on the provision of the law that requires most employers that offer health insurance to their workers to provide the range of preventive health benefits. In both instances, the Christian families that own the companies say that insuring some forms of contraception violates their religious beliefs.
The key issue is whether profit-making corporations may assert religious beliefs under the 1993 Religious Freedom Restoration Act or the First Amendment provision guaranteeing Americans the right to believe and worship as they choose.
The brief from Democratic senators on Tuesday argued that exempting for-profit businesses from the mandate would be "inconsistent" with that 1993 law.