Billionaire investor Warren Buffett's company Berkshire Hathaway has sold nearly half of its stake in General Motors, with experts speculating that the move was prompted by concern over slow electric vehicle launches and uncertainty over United Automobile Workers talks as the potential for a strike looms.

Berkshire Hathaway said it reduced its shares of GM stock from 40 million to about 22 million during the second quarter, according to Monday's quarterly filing with the U.S. Securities and Exchange Commission.

The company did not list a reason for the move, and a phone call to Berkshire Hathaway seeking comment was not immediately returned. GM spokesman David Caldwell declined to comment.

But the sale comes as GM faces a number of challenges. A national rail car shortage, first reported by the Free Press, part of the USA TODAY Network, has impacted all automakers by keeping new vehicles parked at factories. In June, GM CEO Mary Barra said one of the biggest problems she faced was the logistics of getting new cars to dealerships.

GM has also struggled to ramp up production of its EVs this year, citing problems with battery module availability. GM said it is resolving that issue and EV production is expected to improve in the second half.

"We believe this is Buffett cutting some of his stake ahead of a potential bumpy EV launch by GM, which we believe will be successful, but will take some time to play out," said Dan Ives, managing director and senior equity analyst at Wedbush Securities. "Warren is still a big believer in the GM story, we believe, despite this move."

Equity strategist David Whiston at Morningstar Research Securities said Berkshire Hathaway's motivation for selling could be concern over a possible UAW strike, impatience with a stagnant stock price, "to macro risk owning a cyclical name, to just having a better idea and wanting to reallocate capital to that."

"It’s not good, but it doesn’t cause me to worry," Whiston said of Berkshire Hathaway cutting its stake in GM. "Berkshire has owned it a long time and perhaps they are tired of waiting and the UAW risk made them think: Time to move on."

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Wall Street has had a general unease with GM in recent weeks. Last month, GM posted big gains in second-quarter profits, making it one of GM's strongest quarterly earnings results in recent years. Yet, its stock price barely moved prompting Deutsche Bank research analyst Emmanuel Rosner to write in a research note, "Yesterday’s negative market reaction to GM’s solid (second quarter) results and 2023 guidance raise, in our view, reflected some investor concerns that ... there is now limited upside left to (the second half) outlook in light of GM’s higher target, and potential downside risk heading into UAW negotiations."

Rosner specifically cited GM's slow EV launches, the potential for a UAW strike and the risk of economic turbulence hurting the high vehicle prices that have supported GM's profits.

Contact Jamie L. LaReau: [email protected]. Follow her on Twitter @jlareauan. Read more on General Motors and sign up for our autos newsletter. Become a subscriber.