The American automaker estimated that the work stoppage would cost the business about $200 million (£164 million) every week.
Executives declined to comment on when the disagreement over benefits and pay will end.
In September, the United Auto Workers (UAW) union started going on strike against Ford, GM, and Stellantis.
Now over 45,000 workers are taking part in the walkout, which is the first time in the union’s history that all three companies are being targeted simultaneously.
With their most recent declaration, the UAW extended the work stoppage to a GM assembly plant in Texas, employing roughly 5,000 union members. The website produces well-known automobiles like the SUV Chevy Tahoe.
GM expressed its disappointment with the strike’s escalation, labeling it “unnecessary and irresponsible”.