Legislation seeks only voluntary labeling regulations for genetically modified food.
Sixty-eight House members have asked that new inspection rules be withdrawn.
The lawsuit accuses the agency of violating federal law by failing to respond to a 2011 petition.
Sen. Joe Manchin (D-W.Va.) said the FDA "failed" in its duty to protect the public.
Sens. Joe Manchin (D-W.V.) and David Vitter (R-La.) are probing allegations that members of the pharmaceutical industry paid big money to meet with members of the Food and Drug Administration ahead of the agency’s approval of a controversial painkiller.
The sweeping update has been fraught with delays.
New regulations protect workers who report violations under the Food Safety Modernization Act.
Lawmakers say the draft rules for posting nutritional information go too far.
A coalition wants a voluntary federal system that would pre-empt state laws.
The FDA says new user fees on business are essential to its landmark food safety overhaul.