GM's stock on Monday edged down 0.4% to $37.24.
The company and the United Auto Workers continued to negotiate behind the scenes but have been unable to come to terms. The job action began just over a week ago when 49,000 UAW members walked out.
The strike's costs are mounting for GM, which stands to lose $75 million a day based on lost vehicle production and sales, J.P. Morgan analysts estimate.
The estimate is based on GM's ability to roll out two million light vehicles every 261 days, with a profit margin of $10,000 per vehicle, according to published reports.
The strike has already halted production at 30 plants in nine states, with GM forced to shut two Canadian plants, the Associated Press reports.
The two sides remain at loggerheads over profit sharing and wages, the use of temporary workers, and the union's desire to more quickly ramp up new workers, the news service reports.
A big sticking point: GM's plans for the four car-manufacturing plants it wants to close in the U.S., and its proposal to convert at least one factory to battery production. The idea prompts concern about job losses.
Even as GM faces steep losses from the walkout, it could lose even more money if it is forced into a disadvantageous deal, J.P. Morgan warns.
"We are less concerned about costs during the duration of the strike than we are about elevated costs or -- still more important -- any degradation in the flexibility of costs over the life of the four-year contract," the firm's analysts wrote in a note to clients, Business Insider reported.
GM declined comment on the J.P. Morgan report.
"Talks continue and it remains our goal to reach an agreement that builds a stronger future for our employees and our business," a GM spokesperson said in an email.