A spokesman for Mueller told CNN that Mueller did litigation work last year for the entity, called IronBridge, while Mueller was a partner at the WilmerHale law firm. He said the IronBridge work wasn't listed in Mueller's ethics disclosure form released last month by the Justice Department because it didn't meet the threshold for which disclosure is required. Mueller's filing listed multiple major legal clients including Facebook, Apple, Sony Pictures and the National Football League.
"The reporting requirement for public financial disclosure reports requires that you report any source that paid more than $5,000 for your personal services in any calendar year," said Peter Carr, a spokesman for the Special Counsel. "In June 2016 while at Wilmer Hale, Mr. Mueller spent less than half an hour on an IronBridge litigation matter that was handled by another partner. That amount did not meet the reporting requirement."
An attorney for Flynn declined to comment.
IronBridge was one of several consulting companies that were working on the proposed business deal, partnering with the Saudi government and Rosatom, Russia's government-run nuclear energy agency, to build nuclear energy plants in Saudi Arabia.
An attorney representing IronBridge CEO Michael Hewitt didn't immediately respond to a request seeking to clarify whether Mueller's work for IronBridge was connected to the Middle East energy project.
Democrats in Congress this week sent a letter to Mueller
accusing Flynn of failing to disclose a trip he took to push the project, which they alleged would be a legal violation. Mueller has not responded and it is not clear whether the nuclear plants are part of the special counsel investigation.
Hewitt's attorney sent a letter to Democratic lawmakers in July, saying "our clients are not aware of any monetary payments made by IronBridge Group, Inc. or IP3 Corporation to Lieutenant General Michael Flynn."
IronBridge was formed in June 2016, according to Hewitt's attorney, around the time that Mueller did the IronBridge litigation work.
It's not clear whether the legal work for IronBridge would constitute a conflict for Mueller's handling of the Flynn investigation.
The Justice Department has said it reviewed Mueller's past work at WilmerHale and didn't find any conflicts related to his appointment as special counsel. It's not clear whether the IronBridge work was part of that review.
Flynn, a retired Army lieutenant general, was fired weeks into the new administration after providing misleading information to Vice President Mike Pence and others in the White House about his communications with the former Russian ambassador in Washington. But Mueller's focus on Flynn largely centers on work he did for entities connected to the Turkish government and that he didn't disclose. He retroactively registered as a foreign agent for the Turkish work.
The Middle East plan that IronBridge was proposing involved the Saudis selling energy from the nuclear plants to eight other Sunni Arab countries, including Egypt and Jordan. As part of the deal, the countries would also buy military hardware from Russia.
The Treasury Department sanctioned the Russian state-run company in September 2015 for violating US laws prohibiting weapons sales to Iran, Syria and North Korea.