With nearly two-thirds of House Republicans supporting Texas’s lawsuit seeking to overturn the election in the U.S. Supreme Court, a Democratic House member on Friday called the Republicans “traitors” and urged the House’s Democratic leadership not to seat the Republicans when the 117th Congress convenes in January.

The congressman, Bill Pascrell Jr. of New Jersey, cited a Reconstruction-era passage of the 14th Amendment disqualifying elected officials who “have engaged in insurrection or rebellion” against the United States.

“The actions of any of our colleagues to demolish democracy, regardless of party affiliation, must be repudiated in the strongest possible terms,” Mr. Pascrell said in his letter. “The fate of our democracy depends on us.”

Section 3 of the 14th Amendment, known as the disqualification clause, was originally enacted to limit the influence of former Confederates in the Reconstruction era. It has been used occasionally since. Victor L. Berger, a member of the Socialist Party of America, was repeatedly prevented from taking his seat by a House resolution after winning election in 1919 because he had been convicted under the Espionage Act.

House Speaker Nancy Pelosi wrote in a letter to Democrats on Friday that Republicans were “subverting the Constitution by their reckless and fruitless assault on our democracy.”