Battle between House Republicans and firm that produced infamous 'dossier' wages on

— -- Glenn Simpson, co-founder of the investigative firm Fusion GPS, appeared in federal court on Wednesday to fight ongoing efforts to pry more information from his company.

The firm, which produced the so-called “dossier” of unconfirmed and salacious allegations against then-candidate Donald Trump, including purported collusion between the Trump campaign officials and agents of the Russian government, is seeking to thwart efforts by House Republicans to compel the firm's bank to turn over the company's entire financial portfolio -- a move that could reveal its roster of confidential clients.

The funders of the dossier have already been identified – a Republican-backed publication, The Washington Free Beacon, and a law firm for the Democratic National Committee and the Hillary Clinton campaign both acknowledged hiring Fusion GPS to conduct research on Trump – but House Republicans nevertheless renewed subpoenas aimed at opening the firm’s financial records.

Lawyers for the firm have argued that the move is “a poorly disguised effort to harm persons and a business” and filed a temporary restraining order against its bank to prevent them to turning over the records to the committee, while lawyers for the House Republicans argued that the committee’s interest “is not limited to the dossier.”The court order in the case filed in conjunction with Wednesday's appearance is not publicly available, but a source with direct knowledge of the proceedings told ABC News that the judge is still deciding whether to block the bank from handing over the records to the congressional committee. A hearing on the matter is set for November 30th, the source said.

Simpson’s appearance on Wednesday comes just one day after a marathon session on The Hill on Tuesday, when he testified behind closed doors before the House Intelligence Committee for nearly seven hours.

ABC's Matthew Mosk and Benjamin Siegel contributed to this report.