The Ford Motor Co. headquarters stands in Dearborn, Michigan, U.S., on Tuesday, May 22, 2017.  Photographer: Jeff Kowalsky/Bloomberg via Getty Images
CNN  — 

The Justice Department notified four major automakers that it has closed an antitrust investigation involving the companies, launched after they rejected the Trump administration’s relaxed air pollution and mileage regulations, a department official told CNN.

The Department of Justice opened the antitrust investigation last year into BMW, Ford, Honda and Volkswagen and after they agreed to meet the tougher standards set by the California Air Resources Board rather than the administration’s rules, which would roll back standards put in place under former President Barack Obama.

Although the California rules would require automakers to build more costly cars, they gave the companies an advantage: The automakers would have to meet only one national standard, rather than one weaker standard for most of the country and one tougher standard for California and 13 other states that follow its rules. Those 14 states account for about 40% of the US population.

The department’s decision to drop the investigation represents a rare retreat for an administration that has consistently sought to undermine environmental protections and regulations put in place by the Obama administration and progressive state governments. Shortly after the probe was launched last September, the administration revoked California’s authority to set its own vehicle emission standards.

California Gov. Gavin Newsom, a Democrat, called the administration’s move on Friday a “big loss” for President Donald Trump.

“These trumped up charges were always a sham – a blatant attempt by the Trump administration to prevent more automakers from joining California and agreeing to stronger emissions standards,” he said in a statement, adding that the decision is “a victory for anyone who cares about the rule of law and clean air.”

After the deal was struck last year between the four automakers and California, Trump lashed out at the companies in a series of tweets, saying the rolled back federal standards would have made their vehicles cheaper.

Several of the automakers confirmed last year that they had been contacted regarding the investigation, with Ford, Honda and BMW saying they would cooperate with the probe. Only Volkswagen did not confirm the investigation at the time.

This is a breaking story and has been updated.