(CNN) The Russian oligarch Oleg Deripaska, who at one time had financial ties to Paul Manafort, is suing Treasury Secretary Steven Mnuchin and the US Treasury Department over financial sanctions imposed on him amid a congressional crackdown on Russian interests over meddling in the 2016 presidential election.

Deripaska says in court filings that he's lost $7.5 billion of his net worth since he was sanctioned in early 2018. His remaining businesses are near "the brink of collapse," with banks no longer wanting to lend to him and as he has lost business. The Russian government has also threatened to take over some of his businesses, he said in the complaint.

The Trump administration relaxed sanctions on three of Deripaska's major companies -- Rusal, EN+ Group and JSC EuroSibEnergo -- after changes to their ownership structure, though Democrats in Congress have argued that Deripaska still maintains too much influence over the companies.

A spokesman for the Treasury Department said the agency "does not generally comment on pending litigation" and referred questions to the Justice Department.

In the lawsuit, filed in Washington, DC, federal court, Deripaska accuses the Treasury Department of "using the devastating power of US economic sanctions without adhering to the bounds of its legal authority and in a manner that is inconsistent with the US Constitution."

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