(Reuters) - A Ukrainian-American businessman who has ties to President Donald Trump’s personal lawyer cannot rely on executive privilege to shield evidence from prosecutors who accuse him of illegally funneling cash to U.S. political candidates, legal experts said.

A combination file picture shows Ukrainian-American businessman Lev Parnas and Russian born businessman Igor Fruman exiting the United States Courthouse in the Manhattan borough of New York City, U.S., October 23, 2019. REUTERS/Shannon Stapleton/Jefferson Siegel/File Photo

On Wednesday, Lev Parnas pleaded not guilty in Manhattan federal court to using a shell company to donate money to a pro-Trump election committee and illegally raising money for a former congressman as part of an effort to have the president remove the U.S. ambassador to Ukraine.

Rudy Giuliani, Trump’s personal lawyer, has said Parnas and his co-defendant Igor Fruman helped Giuliani’s push to investigate the president’s Democratic political rival, former Vice President Joe Biden, and Biden’s son’s work in Ukraine.

That investigation is at the heart of a Democrat-led impeachment inquiry of Trump, which the Republican president has called a partisan smear.

Giuliani also has represented Parnas and Fruman in personal and business affairs, according to their former lawyer, John Dowd.

Edward MacMahon, an attorney for Parnas, raised the possibility in court on Wednesday that some evidence against his client might be protected by executive privilege, noting that Giuliani worked as Trump’s lawyer while representing Parnas.

But legal experts said the privilege cannot be used to shield documents from prosecutors in the criminal case. The privilege, which allows a president to block information from being shared with other branches of government, typically covers private discussions a president has with White House advisers, or internal discussions among executive branch officials. Photos have surfaced of Parnas and Fruman with Trump, but the president has said he does not know the men and that he often poses for photos.

David Sklansky, a former federal prosecutor, said the privilege is limited to communications inside the executive branch and would not apply to communications between Trump and Giuliani.

Giuliani was acting as a private adviser for Trump and not part of the White House, said Sklansky, a professor at Stanford Law School.

John Yoo, a law professor at the University of California at Berkeley, agreed.

“I don’t think they have any plausible claim to protection under any kind of executive privilege or immunity,” Yoo said.

MacMahon and Joseph Bondy, another attorney for Parnas, declined to comment.

Legal experts said Parnas might have better luck arguing that some documents are covered by attorney-client privilege, which protects communications between lawyers and clients. Parnas’ lawyer raised that possibility in court as well.

A prosecutor said on Wednesday that the government has arranged for a group of lawyers known as a “filter team” to review potentially privileged communications.

But the complicated nature of Giuliani’s relationship with Parnas would made it difficult to claim communications should be kept from prosecutors, the experts said.

Giuliani has told Reuters he was paid $500,000 to consult on technology and provide legal advice on regulatory issues in connection with a company Parnas helped found.

Peter Joy, a professor of criminal law at Washington University in St. Louis, said communications between Giuliani and Parnas could be protected by attorney-client privilege only if they were kept confidential and made for the purpose of seeking or giving legal advice.

Discussions between the two men in furtherance of Giuliani’s Biden-related efforts in Ukraine were unlikely to be protected, he said.

“It is not legal work to try to get opposition information,” Joy said.

Communications aimed at furthering an illegal act also are not covered by attorney-client privilege, said Daniel Medwed, a professor of criminal law at Northeastern University School of Law.

Prosecutors said Parnas and Fruman conspired to contribute foreign money including at least $1 million from an unidentified Russian businessman to candidates for federal and state offices to buy influence. U.S. law prohibits foreign donations in American elections.

“If it turns out these communications related to a crime or fraud, then the privilege claim is not going to fly,” Medwed said.