The United Auto Workers is preparing to ask its members to authorize a strike, as negotiations between the union and Detroit’s Big Three auto manufacturers stall out.

For months, the union has been negotiating with the Big Three — Ford Motor Company, General Motors, and the parent company of Chrysler, Stellantis. The UAW president, Shawn Fain, however, says the pace of negotiations has been far from sufficient.

Mr. Fain hosted a Facebook Live session Tuesday night to “address the slow pace of negotiations and announce preparations for strike authorization votes to be held next week by 150,000 UAW members at Ford, General Motors and Stellantis,” according to a union news release.

“Whether or not there’s a strike next month is entirely up to the Big Three automakers,” Mr. Fain said. “Our priorities are clear, the companies can afford them, and there’s plenty of time for the Big Three to get serious about these negotiations.”

During the Facebook Live session, Mr. Fain expressed solidarity with striking writers and actors in Hollywood, saying that “all of us are at war with corporate greed.”

Some of the demands of the union include higher pay, cost-of-living adjustments, an increase in benefits for current retirees, and the inclusion of employees who work at electric vehicle manufacturing facilities in the UAW collective bargaining agreement.

The UAW is demanding a 46 percent boost to pay for the union members, which would bring the top union wage to $47.14 an hour from $32.32 an hour. According to ZipRecruiter, the average wage of a UAW member is about $25 an hour.

Mr. Fain has pointed to the compensation of the General Motors chief executive, Mary Barra, who saw a 34 percent compensation increase between 2021 and 2022, with her total pay rising to $29 million, as evidence that the Big Three can afford pay raises.

Mr. Fain has also suggested that the union would fight for a 32-hour work week and demand that the companies guarantee that current members get defined-benefit pensions.

With efforts to approve the strike under way, the union could authorize one as soon as August 24. The current collective bargaining agreement between the UAW and the Big Three expires on September 14.

In a letter to employees last week, Stellantis’s chief executive, Mark Stewart, accused Mr. Fain of “theatrics and personal insults” and claimed that the company is committed to a new agreement based on “economic realism.”

“Mr. Fain’s demands could endanger our ability to make decisions in the future that provide job security for our employees,” Mr. Stewart wrote.

A Stellanis spokeswoman, Jodi Tinson, struck a less aggressive note, telling the Sun in a statement, “The discussions between the company and the UAW’s bargaining team continue to be constructive and collaborative with a focus on reaching a new agreement that balances the concerns of our 43,000 employees with our vision for the future.”

A spokesman for General Motors, David Barnas, also provided a statement to the Sun in the wake of Mr. Fain’s Facebook Live stream, saying, “We’ve been working hard with the UAW every day to ensure we get this agreement right for all our stakeholders.”

“We know that our U.S. economic impact supports more than six jobs for every job created by GM,” Mr. Barnas said. “We take that responsibility very seriously, and we continue to bargain in good faith each day.”

A Ford spokeswoman, Kelli Felker, said in a statement to the Detroit Free Press that the company looks forward “to working with the UAW on creative solutions during this time when our dramatically changing industry needs a skilled and competitive workforce more than ever.”