The bipartisan Senate Ethics Committee voted unanimously on Monday to advance an inquiry into Senator Robert Menendez of New Jersey, signaling that it was moving swiftly to lay the groundwork to potentially expel him after his federal bribery conviction last week.

In a statement, the committee said its work had progressed to an “adjudicatory review,” meaning that its members had found “substantial cause” to believe Mr. Menendez had violated the law or Senate rules.

The vote will almost certainly increase pressure on Mr. Menendez, a Democrat, to resign, by showing that his colleagues are serious about threats to hold an expulsion vote if he does not step down voluntarily.

“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 committee’s leaders, Senators Chris Coons of Delaware and James Lankford of Oklahoma, wrote in the statement.

The Senate’s gravest form of punishment, expulsion has not been used since the 19th century and requires the support of two-thirds of senators. But a growing number have said it is warranted by Mr. Menendez’s conviction on all counts in a sweeping bribery scheme involving a foreign power and bars of gold.

Mr. Menendez, 70, has maintained his innocence and vowed to appeal the guilty verdict. The New York Times reported last week that he had told allies he was considering stepping aside rather than face the ignominy of an expulsion vote. But Democrats in Washington and New Jersey worried that he might be preparing to dig in for a longer fight.