The United States Department of Justice has launched a preliminary anti-cartel investigation into the practices of automotive giants Ford, Honda, BMW and Volkswagen, Wall Street Journal reported on Friday.

The companies are investigating an independent agreement they have reached with California to exceed the emission standards for gas, according to financial sources familiar with the matter.

Justice Department lawyers want to determine whether the four car companies have violated federal competition law by agreeing to follow harmful emissions standards beyond those proposed by Presidential Administration Donald Trump.

The deal was announced in July in collaboration with California's air quality officials, and likely contradicts the policies of President Trump's administration. The Washington government is seeking to reduce regulations in the automotive industry, but at the same time wants to regulate automobile gas emissions at the federal level.

At this stage, Ford, BMW and Volkswagen haven’t commented on Wall Street Journal information.

Honda said, "Our company will work with the Department of Justice on the recent agreement on emissions from the state of California and various automakers, including Honda."