Texas’s attorney general, Ken Paxton, said on Friday that the state bar plans to sue him over his efforts to overturn Donald Trump’s defeat in the 2020 presidential election by falsely claiming there had been widespread voter fraud in battleground states.

In December 2020, the US supreme court unanimously rejected a baseless lawsuit filed by Paxton on behalf of Texas seeking to scotch Joe Biden’s win in the election the previous month.

All nine justices on America’s highest court dismissed the long-shot effort in the Texas lawsuit that was aimed not at the result in that state but sought to throw out the vote counts in four vital states that the president lost: Georgia, Michigan, Pennsylvania and Wisconsin.

The unanimity from the court came despite the bench featuring a six-to-three supermajority of conservative-leaning judges, three nominated by Trump.

The bar complaints against Paxton alleged that his petitioning the US supreme court to overturn the 2020 election was frivolous and unethical.

Paxton announced the development with the state bar on Friday, raising yet another legal danger as the embattled Republican is locked in a primary runoff.

Since last summer, the state bar of Texas has been investigating complaints over Paxton’s petitioning of the supreme court to block Biden’s victory.

The professional group has not publicly filed a suit but Paxton, saying it plans to bring one against him and his top deputy, suggests the agency may believe their actions amounted to professional misconduct.

The attorney general said he stood behind his challenge to the “unconstitutional 2020 presidential election”, even as he blasted the bar and announced an investigation into a charitable group associated with it.

“I am certain that the bar will not only lose but be fully exposed for what they are: a liberal activist group masquerading as a neutral professional association,” Paxton said on Twitter.

The bar, which is a branch of the Texas supreme court, said in a statement that “partisan political considerations play no role” in its actions.

State law prohibits it from discussing investigations unless a public complaint is filed and a spokesperson declined to comment.

In bringing a court action against an attorney, the bar can seek punishment ranging from a written admonition to suspension or disbarment.

The discipline process resembles a trial and could include both sides taking testimony and obtaining records through discovery.

In addition to the unanimous decision by the US supreme court, at the time the justice department, under Trump’s attorney general, Bill Barr, found no evidence of fraud that could have changed the election’s outcome.

Paxton forecast the legal action against him during the final weeks of his Republican primary runoff against the state land commissioner, George P Bush.

A two-term incumbent, Paxton drew an unusual number of primary challenges after eight of his top deputies told the FBI in 2020 that the attorney general had been using his office to benefit a wealth donor.

They accused him of bribery, abuse of office and other crimes, prompting a federal investigation.

Paxton has denied wrongdoing and separately pleaded not guilty in a state securities fraud case that has languished since 2015. His defense lawyer, Philip Hilder, declined to comment.