(Reuters) - Rudolph Giuliani is now facing at least two New York disciplinary complaints by prominent attorney groups citing his repeated voter fraud claims on behalf of former president Donald Trump and his incendiary remarks just before the Jan. 6 storming of the U.S. Capitol.

The latest complaint, filed Thursday by Michael Miller, a past president of the New York State Bar Association, the New York County Lawyers Association, and 55 other attorneys, law professors and retired judges, comes after a group called Lawyers Defending Democracy submitted a similar complaint this week.

In both complaints, the lawyers target Giuliani for seeking to invalidate millions of ballots cast in Pennsylvania during the election based on unsubstantiated claims of election fraud. Both also cite his speech to a crowd of Trump's supporters encouraging "trial by combat" just before they marched to the Capitol.

"The complaint speaks for itself," Miller said. "We believe Mr. Giuliani egregiously violated several rules of professional conduct."

Miller and his co-complainants are being represented by Ronald Minkoff, the chair of Frankfurt Kurnit Klein + Selz's professional responsibility group.

Klaus Eppler, a partner at Proskauer Rose; John Kiernan, the ethics committee chair at Debevoise & Plimpton; and James Kobak, Jr., senior ethics counsel at Hughes Hubbard & Reed, are also among the signatories.

Minkoff said the complaint will be investigated by the attorney grievance committee of the New York First Judicial Department. The proceedings are secret pending the court's final decision, he added.

The committee has the power to discipline lawyers, including revoking their law license. Giuliani did not respond to a request for comment.

In addition to accusing Giuliani of spreading false claims and incendiary rhetoric, Miller and the other complainants said Giuliani "traded on his reputation to support these falsehoods – publicly referencing his stature as a lawyer."

Giuliani's prominence as a former U.S. attorney and mayor of New York City elevated his outlandish claims that undermined the foundation of democracy, the complainants wrote.

"In doing so, Mr. Giuliani played a part (if not a substantial role) in inciting what would become the most egregious breach of our nation's Capitol Building since the war of 1812 - a clear violation of 8.4(d)," they wrote, referring to the rule that prohibits lawyers from engaging in conduct that is "prejudicial to the administration of justice."

Wednesday's letter from Lawyers Defending American Democracy was initially signed by 40 attorneys, including former federal prosecutors and judges and current attorneys at Gibson, Dunn & Crutcher, Jackson Walker, Morrison & Foerster, and Wilson Sonsini Goodrich and Rosati, among other major firms.

Online, the list of signatories had grown to more than 4,200 people, including lawyers and non-lawyers, by Friday afternoon.