The United Auto Workers union blasted General Motors Tuesday for considering selling Chinese-built Buick Envisions in the United States and vowed to try to kill the plan during ongoing contract negotiations.

"After the sacrifices made by US taxpayers and the US workforce to make General Motors the profitable quality company it is today, UAW members are disappointed with the tone-deaf speculation that the Envision would be imported from China," said Cindy Estrada, the UAW vice president responsible for the union's relations with GM.

"GM should stand by its declaration that it will build where it sells," Estrada said in a statement.

"The Envision should be made in the US by the workforce that saved GM in its darkest time, and UAW members intend to address this issue in contract talks."

GM spokesman Nick Richards said reports about importing the Envision, a compact sport utility vehicle GM put on sale in China in 2014, are "speculative."

"We have not announced the Buick Envision for any markets other than China, where it has been extremely successful to date," he told AFP. "As a matter of practice, we don't discuss future product plans."

GM also declined to comment on reports that in 2016 it would shift production of the Buick Verano sedan from Michigan to China; production of the Buick Regal from Canada to either China or Europe; and also start importing the Buick Cascade convertible from Europe.

The speculation comes as Republican presidential frontrunner Donald Trump has seized on trade with China as a campaign issue and called for leveling a 25 percent tariff on Chinese imports.

Buick is one of GM's most popular brands in China and the automaker sell roughly four Buicks in China for every Buick it sells in North America.

But car sales are slowing in China, where the Detroit-based carmaker has installed a huge production base over the past decade.

The UAW is currently in the midst of negotiating new labor pacts with GM, Ford and FCA, which owns the Chrysler brands.

Union president Dennis Williams has said a pay raise is the union's top priority. However, the potential for lost jobs and production will certainly complicate talks, especially after both GM and Ford announced major investments in Mexico.

A substantial portion of all the vehicles built in Mexico are exported to the United States.

GM chief executive officer Mary Barra told reporters in June that she would not negotiate with the UAW in public and preferred to keep any discussions behind closed doors -- a policy both sides have adhered to since talks began last month.