Senator Bernie Sanders, independent of Vermont, said the “so-called conference committee,” as he put it, “is a farce.”

Members of the committee assembled for their public session in a basement meeting room in the Capitol, and the partisan skirmishing began right at the outset.

Representative Richard E. Neal of Massachusetts, the top Democrat on the Ways and Means Committee, asked that the conference committee postpone its work until Doug Jones, the winner of Tuesday’s special election for Senate in Alabama, is sworn into office.

The lawmaker presiding over the meeting, Representative Kevin Brady, Republican of Texas and the chairman of the Ways and Means Committee, said the motion was not allowed.

Representative Lloyd Doggett, Democrat of Texas, quickly clashed with Mr. Brady over his handling of the meeting, reminding him that the session was not being conducted under “Putin rules.”

Democrats also denounced the substance of the tax overhaul.

“The American people are witnessing a master class in how one political party, relying on secrecy, distortion and brute force, can muscle an unpopular, deficit exploding corporate giveaway to passage,” Mr. Wyden said. “This is the ultimate betrayal of the middle class.”

The gathering will be one of the final times that Democrats will be able to publicly criticize the tax legislation while being face-to-face with the Republicans who are crafting it. Thus far, they have largely assailed the partisan process and argued that the bill benefits the rich and corporations and doesn’t do enough to help the middle class.