Their news conference, set for 11:30 a.m. ET (1630 GMT), comes two days after a nonpartisan watchdog accused Santos of breaking campaign finance laws in a filing with the Federal Elections Committee.

The Nassau County, New York, Republican Party, from the New York City suburb that includes the majority of Santos' district, said dozens of county Republican officials would make "a major announcement regarding the disgraced Member of the House of Representatives."

"The contingent of elected officials, candidates and party officials will deliver the strongest statement yet regarding the Nassau GOP's position on Santos," the party added in a statement.

Santos has admitted fabricating much of his resume.

Republicans currently hold a narrow 222-212 majority in the U.S. House of Representatives. He won his November race over Democrat Robert Zimmerman by a margin of 7.5 percentage points.

But his victory was quickly overshadowed by media reports indicating that the persona he presented to voters was largely a work of fiction.

Among other claims, Santos said he had degrees from New York University and Baruch College, despite neither institution having any record of him attending. He claimed to have worked at Goldman Sachs and Citigroup, which was also untrue.

He also falsely said that he was Jewish and that his grandparents escaped the Nazis during World War Two.

Two House Democrats on Tuesday referred the matter to the House ethics committee this week. The local district attorney has said her office is investigating Santos.

No. 2 House Republican Steve Scalise told reporters on Tuesday that the party was looking into the matter.

"This is something that's being handled internally," Scalise told reporters on Tuesday. "Obviously there were concerns about what we had heard and so we're going to have to sit down and talk to him about it."

(Reporting by Gram Slattery; Editing by Scott Malone and Mark Porter)

By Gram Slattery