The Department of Justice (DOJ) is dropping its investigation into four major automakers that sided with California over the Trump administration on emissions standards, a person familiar with the matter confirmed to The Hill.

The probe, announced in September, focused on BMW, Ford, Volkswagen and Honda and examined whether the companies violated the law by agreeing to follow stricter emissions standards advocated by California rather than ones determined by the federal government.

California Gov. Gavin Newsom Gavin NewsomCalifornia family frustrated that governor, Harris used fire-damaged property for 'photo opportunity' Pac-12 moves toward 'return to competition' after Big Ten announces resumption of football season Ben Shapiro's Daily Wire leaving California: 'Terrible governance has consequences' MORE (D) celebrated the news on Twitter on Friday, calling it a "sham" probe and saying that the decision to close the investigation was a "'HUGE' win for anyone who cares about" the law and the air.

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The investigation looked at whether the companies' agreement reached last summer with California unfairly stifled auto sale competition in the state.

The administration faced pushback over the probe from state officials and Democratic lawmakers, who viewed the investigation as politically motivated.

The Environmental Protection Agency (EPA) and the Transportation Department sent a joint letter to California regulators in early September warning of "legal consequences" over the state's agreement with the four automakers.

However, Assistant Attorney General Makan Delrahim, head of the DOJ's antitrust division, pushed back on the criticism, maintaining that the probe was not politically motivated and that "the Department of Justice’s sole consideration is the law."

“Those who criticize even the prospect of an antitrust investigation should know that, when it comes to antitrust, politically popular ends should not justify turning a blind eye to the competition laws,” he wrote in a USA Today op-ed in September.

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California and the administration have battled for months amid President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE's planned rollback of national fuel efficiency standards.

In September, the Trump administration revoked California's authority to set its own stricter emissions standards for vehicles, prompting a legal challenge from California and 23 other states.

The EPA also threatened to withhold highway funding from the state unless it handled a decades-long backlog of air pollution plans.

The administration is expected to finalize its emissions rule in the coming weeks to roll back Obama-era standards. The original rules called for roughly 54 miles per gallon by 2025. The Trump administration's rules would reportedly bring that closer to 40 miles per gallon.