Skadden, Arps, Slate, Meagher & Flom's controversial work for the former government of Ukraine is part of an investigation by the Justice Department, which is asking the firm to produce documents on its work, according to a report by The New York Times on Thursday.

Skadden's work was already under public scrutiny from several media reports in the last year. Skadden was paid more than $1 million in legal fees after putting together a December 2012 report that critics said effectively justified the jailing of a Ukrainian political rival, former Ukrainian Prime Minister Yulia Tymoshenko, according to media reports.

The Skadden report found that while some of the charges against Tymoshenko were procedurally flawed, there was no political motivation behind her seven-year prison sentence.