(CNN) Special Counsel Robert Mueller appears to be relying on an obscure 218-year-old law to apply pressure to officials in pursuit of a broader investigation into Russia's interference in the presidential election, though experts doubt prosecutors would ever use it to seek charges.

In court filings, Michael Flynn acknowledged he lied to the Federal Bureau of Investigation about calls with foreign officials, including the Russian ambassador, to try to influence the outcome of a UN resolution in December 2016 while a member of President-elect Donald Trump's transition team.

Michael Zeldin, a former prosecutor who was a special assistant to Mueller in the Justice Department, said the outreach to foreign governments by Trump's team at the time the Obama administration was in dispute with Israel over the vote is "facially" a violation of the Logan Act

Flynn's contact with the Russian ambassador "seems to violate what the Logan Act intended to prevent," Zeldin said. He added that even though the Logan Act hasn't been used successfully "it doesn't mean that Mueller wouldn't consider using it to pressure defendants."

The Logan Act, which was passed in 1799, forbids private citizens "without authority of the United States" from negotiating with foreign governments with an "intent to influence" measures or conduct of that government regarding any "disputes or controversies."

No one has been successfully prosecuted for violating the Logan Act, which Congress passed in response to the actions of George Logan, a Pennsylvania doctor who went to France as a private citizen and tried to negotiate with officials there, according to the Congressional Research Service . Lawyers say there are questions about the constitutionality of the law pertaining to its vagueness and the First Amendment right to free speech.

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"I think it's a pressure point for other related offenses," said Stephen Vladeck, a professor at the University of Texas law school and a CNN contributor. "At the end of the day, there's no way in which any indictment is going to rise and fall on the Logan Act. The question is whether there's some broader conspiracy. It increasingly looks like a pretty wide-reaching cover up."

Lawyers say the conversations could also be used by Mueller's team as it looks for possible evidence of conspiracy, a quid pro quo between Trump campaign officials and Russians or pursues a case of obstruction of justice. In court filings, Mueller's team stated: "Flynn's false statement and omissions impeded and otherwise had a material impact on the FBI's ongoing investigation into the existence of any links or coordination between individuals associated with the campaign and Russia's efforts to interfere with the 2016 presidential election."

A senior White House official on Friday defended Flynn's conversations and claimed the Obama White House knew about the discussions. "None of the conversations were improper and were authorized by the Obama administration," the official said.

Court filings show that Flynn said he was directed by a "very senior member of the presidential transition team" to make contact with foreign governments, including Russia, on December 22, 2016, to "delay or defeat a UN resolution to condemn Israeli settlements."

A source familiar with the investigation said that Jared Kushner, Trump's son-in-law and senior adviser, is the "very senior" transition official mentioned in the documents. Kushner met with Mueller's investigators last month to discuss Flynn, CNN has reported.

The following day, the Russian ambassador told Flynn Russia would not vote against the resolution. The resolution passed.

An attorney for Kushner did not comment.

CNN reported at the time that the Israeli government reached out to Trump for help in pressuring the Obama administration to veto a UN Security Council resolution condemning settlement activity. But the Israeli official told CNN that his country also approached the Trump campaign after it felt that it had failed to persuade the Obama administration to veto the planned vote. The official said that Israel "implored the White House not to go ahead and told them that if they did, we would have no choice but to reach out to President-elect Trump."

Shortly after the vote, Trump tweeted : "As to the U.N., things will be different after Jan. 20th."

One day after the vote, Trump condemned it on Twitter : "The big loss yesterday for Israel in the United Nations will make it much harder to negotiate peace. Too bad, but we will get it done anyway!"

Flynn also admitted to making false statements to the FBI about conversations he had with Kislyak beginning on December 28, 2016, about sanctions enacted by the Obama administration. In one call, Flynn discussed with "a senior official" on the Trump transition team who was with other transition officials at Trump's Mar-a-Lago resort that they not want Russia to escalate the situation in light of the sanctions.

The following day, Russian President Vladimir Putin said Russia would not retaliate against the US for the sanctions.

KT McFarland was the senior transition official at Mar-a-Lago who was described as discussing with Flynn what, if anything, to communicate to the Russian ambassador about US sanctions, according to sources familiar with the matter.

An attorney for McFarland declined comment.