She claims managers harassed and demoted her for reporting production defects, including faulty seat belts and brakes.
Katy Cameron, 54, an employee since 1985 of NUMMI in Fremont, California alleges that NUMMI managers altered her reports to delete references to defects that might harm the automakers image with consumers.
Cameron claims that the cover-up included minor flaws and major mistakes that could have resulted in physical harm and injury to purchasers.
The lawsuit says her reports included defective seat belts, non-functioning headlights, turn signals, inadequate brake, steering and transmission fluid.
A spokesman for Toyota said the company would not discuss the lawsuit while insisting that quality has never been compromised in the California plant.
NUMMI builds the Toyota Corolla sedan and Tacoma pickup as well as the Pontiac Vibe.
Cameron claims in the lawsuit that she reported between nine and 15 defects per vehicle during 2005 and 2007. The lawsuit alleges that managers became concerned that she might send copies of her reports to Toyota officials and tried to fire her as a result.
She claims the company demoted her to the assembly line and ordered her to undergo mental fitness evaluations because of her quality control reports.