Negotiators for General Motors and the United Auto Workers held their first high-level negotiations in four days Friday — but it wasn’t a warm reunion, The Post has learned.

The UAW on Friday morning called for top union and company representatives to gather for an 11 a.m. “main table” meeting at Detroit Renaissance Center — in part to object to recent negotiating tactics by the Big Three automaker, according to a person familiar with the negotiations.

Union brass are upset that GM went over their heads in a bid to end the 26-day strike with a letter sent directly to the union’s 46,000 striking members. The meeting, which lasted about an hour, was at times “very tense,” according to the source.

The letter, by GM executive Gerald Johnson, included previously undisclosed details of GM’s latest offer to the union, including plans to increase its investment in US facilities to about $9 billion, up from $7 billion, according to the Wall Street Journal.

The letter also blasted the UAW for dragging its feet on accepting an offer, which GM said includes pay increases, improvements in yearly profit-sharing payouts for hourly workers and no increase to workers’ out-of-pocket health care costs.

Union officials are objecting to the company’s characterization of the company’s latest offer, which they say hasn’t materially changed since the strike began 26 days ago.

“Let me be clear that the company’s strategy of releasing half-truths does nothing to reach a final settlement for you and your families,” UAW vice president Terry Dittes said in a video response to members Friday.

UAW officials have been pushing for the company to move entire auto manufacturing lines to the US from Mexico, which they say will increase job security.

The high-level talks come two days after GM CEO Mary Barra held a secret meeting with Dittes, who’s leading the main talks, and UAW president Gary Jones — urging them to end the strike.

GM, however, contends that the ball is in the union’s court, since they were the last ones to have made a formal offer, on Monday, Oct. 7, according to a source close to the company.

The UAW put in its formal offer on Saturday, Oct. 5, including demands for GM to move some manufacturing from Mexico to the US. No new formal offers are expected to be presented by UAW officials, according to one source familiar with the talks. A person familiar with the negotiations declined to say why.

The extended strike has been a drag on both the company and its workers, who have been subsisting on $250 a week in strike pay — far less than what they would normally get. They missed a third paycheck Friday.

The maker of Cadillac and Chevrolet cars, meanwhile, has lost about $1.5 billion since the work stoppage, according to a new analysis by Credit Suisse. Wall Street is also predicting that the strike could force credit rating agencies like Moodys Investor Services to downgrade the company’s debt to junk status.

Representatives for the UAW declined to comment. A spokesman for GM also declined to comment.