But Pampa Calichera, Potasios de Chile and Global Mining – which together control a majority stake in SQM – allege the five-member court had approved the deal “practically in secret.”

“The opportunity given to my clients to learn, understand and then opine on a deal worth more than $4 billion, which generates enormous competitive risks for SQM, was five days, and nothing more,” lawyers for the shareholders wrote in the lawsuit.

The three shareholders, known collectively as the Pampa Group and controlled by SQM’s former president, Julio Ponce, asked the court to “urgently suspend” the agreement between regulators and Tianqi.

The three shareholders, known collectively as the Pampa Group and controlled by SQM’s former president, Julio Ponce, asked the court to “urgently suspend” the agreement between regulators and Tianqi

Tianqi did not immediately reply to requests for comment.

Tianqi’s interest in acquiring the stake in SQM comes as Beijing is aggressively promoting electric vehicles to combat air pollution and help China’s domestic carmakers leapfrog the combustion engine to build global brands.

The agreement between Chile’s antitrust regulator and Tianqi stipulates that the Chinese miner cannot name any of its executives or employees to SQM’s board, and requires it notify regulators of any future, lithium-related deal struck with either SQM or rival and top lithium producer Albemarle.

Prior to its approval, SQM had objected to the deal on the grounds it did not go far enough to limit Tianqi’s access to corporate secrets and sensitive information.

Chile’s antitrust regulator launched an investigation in June, shortly after Tianqi said it would buy 24 percent of SQM for $4.1 billion, giving it a stake in one of the world’s top producers of lithium, a key ingredient in the batteries that power everything from cellphones to electric vehicles.

(By Dave Sherwood; editing by Jonathan Oatis)