The Senate returns Tuesday as uncertainty looms over the future of Sen. Bob Menendez following his conviction on federal corruption charges, with some members of the Democratic caucus calling for his expulsion if he does not step down.

The 70-year-old New Jersey Democrat has defied calls from fellow Democrats to resign, including from key leadership voices like Senate Majority Leader Charles E. Schumer of New York.

Democrats ramped up pressure on Menendez last week after a federal jury found him guilty on 16 counts, including bribery, extortion and acting as a foreign agent, in a case where the Justice Department accused him and his wife of taking bribes from New Jersey businessmen.

And on Monday, the Senate Ethics Committee notified Menendez’s counsel that panel members unanimously voted to start an adjudicatory review of alleged violations of Senate rules, according to a joint statement from the panel’s top lawmakers, Sens. Chris Coons, D-Del., and James Lankford, R-Okla.

The review, they said, is required when the panel considers disciplinary actions, such as a censure or expulsion.

Coons and Lankford said the committee expects to complete the adjudicatory review “promptly.”

“At the completion of the adjudicatory review, the Committee will move expeditiously to submit a written report to the Senate including specific findings and any recommendations for disciplinary action,” the two lawmakers said.

As some lawmakers call for his resignation, other Democratic colleagues say that Menendez should be expelled from the post if he does not step down.

That includes New Jersey Democratic Sen. Cory Booker, who said he would lead an effort.

“For New Jersey, this is a painful day of real heartbreak, and frankly, just deep disappointment. A jury that was sworn to objectivity, a jury of his peers, found by the highest criminal standard — beyond a reasonable doubt — that he was guilty on all 16 charges,” Booker said in an interview with MSNBC on the day of the verdict.

Removing Menendez would be a historic move for the Senate, which has successfully expelled only 15 members, nearly all of which occurred during the U.S. Civil War era.

The last time the Senate considered expulsion was 1995, when Sen. Bob Packwood, R-Ore., announced his resignation the day after the Ethics Committee recommended he be expelled amid accusations of sexual misconduct and abuse of power, according to the Senate’s website.

An expulsion effort could also eat up valuable time and attention when the chamber is scheduled to be on recess for most of the month of August and all of October.

Several Democrats also said Menendez should face expulsion if he does not step down, including Sens. Jacky Rosen, D-Nev., Debbie Stabenow, D-Mich. and Bob Casey, D-Pa.

Sen. Tammy Baldwin, D-Wis., said she’s prepared to expel him. “No one is above the law and the crimes Senator Menendez was found guilty of violate the American people’s trust and have compromised his ability to effectively represent his constituents,” Baldwin said in a statement.

At trial, the jury heard from an FBI agent who discussed how federal authorities found gold bars and hundreds of thousands of dollars in cash during a search of a New Jersey residence that Menendez shared with his wife.

An insurance broker, who pleaded guilty in the case, also testified at trial that he bribed the senator in a bid to influence state-level investigations to benefit people close to him. After the verdict, an attorney for Menendez, said they will pursue all appellate avenues “aggressively.”