DETROIT (CBS DETROIT/ AP) — An investigation is being conducted by the U.S. Justice Department of four automakers.

The four automakers have signed on with California in a deal to toughen tailpipe emissions standards.

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The Justice Department would not comment on the investigation.

Ford received a letter from Justice informing it of the investigation.

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The company’s spokesman, T.R. Reid confirmed Friday that the company is cooperating in the inquiry.

In July, Ford, Honda, Volkswagen and BMW reached a deal with California to abide by standards that are tougher than those preferred by the Trump administration. The standards are closely linked with fuel economy requirements.

The move bypasses Trump’s push to relax pollution and mileage standards nationwide that were set by the Obama administration.

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