On Monday, he said the Trump lawsuit was not a surprise given Mr. Trump’s “long history of trying to use baseless lawsuits to attack his adversaries,” but he argued that neither he nor his businesses had a “valid legal basis to interfere with this duly authorized subpoena from Congress.”
“This complaint reads more like political talking points than a reasoned legal brief, and it contains a litany of inaccurate information,” Mr. Cumming said, accusing the White House of across-the-board stonewalling of his committee.
The accounting company, which prepared financial statements for loan applications for Mr. Trump, had indicated to the chairman that it would comply with an earlier, voluntary request for that information only if he issued a subpoena. And in a statement last week, it said, “Mazars USA will respect the legal process and fully comply with its legal obligations.”
On Monday, a spokeswoman for Mazars declined to comment on the suit but said the company would “respect this process and will comply with all legal obligations.” It was unclear if it still intended to fulfill the subpoena by an April 29 deadline set by Mr. Cummings.
After the subpoena was issued, lawyers representing Mr. Trump in the congressional inquiries, William S. Consovoy and Stefan Passantino, made arguments similar to those laid out in the lawsuit directly to Mazars, urging the company not to comply. Republicans on the Oversight committee have made similar arguments.
Mr. Cummings is not the only Democratic chairman pursuing details of Mr. Trump’s long-obscured finances. The Intelligence and Financial Services committees have each issued subpoenas to other financial institutions, including Deutsche Bank, a longtime lender to Mr. Trump’s businesses.
And the House Ways and Means Committee has demanded six years of tax returns filed by Mr. Trump and his businesses. The committee has set a Tuesday deadline for the Internal Revenue Service to comply with the demand, filed not by subpoena but under a provision in the tax code that says the I.R.S. “shall” comply with requests from the chairman of the House and Senate tax-writing committees.
Democrats’ increasingly invasive requests for financial records and other documentation have irked executives at the Trump Organization, according to a person familiar with their thinking. The company cooperated with numerous requests from Congress and other investigators for records related to Russia and its election interference efforts, but they believe the financial requests have gone a step too far.