Among the accusations in the charging documents are allegations that Santos applied for unemployment benefits during the pandemic, falsely claiming to have been unemployed since March 2020, according to prosecutors.

He collected money from then until April 2021, "when Santos was working and receiving a salary on a near-continuous basis and during his unsuccessful run for Congress," referring to his first run for the job, which he lost. In total, prosecutors say he collected more than $24,000 in benefits.

He was actually being paid a $120,000 salary as regional director of an investment firm at the time, according to prosecutors.

Santos left Washington, D.C., on Tuesday and drove up to New York to surrender.

Before leaving, Santos met with House GOP leader Kevin McCarthy's staff and informed them that he would be charged.

He's expected to plead not guilty, sources told ABC News.

Santos met with the FBI at an off-site location Wednesday morning and surrendered to authorities.

In one story of alleged misdeeds, as ABC News previously reported, the FBI contacted a Navy veteran, Richard Osthoff, about a GoFundMe campaign Santos established to raise money for the veteran's service dog.

Santos established the GoFundMe account under the auspices of a charity, Friends of Pets United, and raised $3,000 to help Osthoff pay for surgery to remove a tumor from the dog, sources said.

But Osthoff told ABC News Santos did not come through with the money and ignored text messages about it. The dog, Sapphire, subsequently died.

These allegations are not included in Wednesday's indictment, however.

Santos insisted earlier this year he would serve out his term despite mounting controversies surrounding his past falsehoods, scrutiny of his finances, and multiple investigations.

Santos, who has admitted to fabricating parts of his biography, has denied any criminal wrongdoing.

Investigators have been focusing on Santos' financial disclosures, according to sources.

In a series of campaign disclosure amendments filed in January, Santos marked two loans that he had previously reported as loans from himself -- $500,000 from March 2022 and $125,000 from October 2022 -- as not from "personal funds from the candidate."

In a previous version of his campaign disclosure, the $500,000 was reported as a loan from George Anthony Devolder-Santos, with a checked box indicating it was from "personal funds of the candidate." But in an amendment to that report filed earlier this year, that box was left unchecked.

Santos, who was elected in November to represent New York's 3rd Congressional District, has been under mounting scrutiny over his finances -- with 2022 disclosures indicating millions in assets after previously disclosing less than $60,000 in income in 2020.

-ABC News' Soo Rin Kim

About a dozen GOP members of the House had previously called on Santos to resign or be expelled from Congress in the face of allegations against him, and several of them are reiterating that stance today.

In a statement today, fellow New York Rep. Nicole Malliotakis, said, "The charges against Rep. Santos are extremely serious and deeply disturbing and as I've previously said, he simply doesn't have the trust of his constituents or colleagues. The sooner he leaves, the sooner his district can be represented by someone who isn't a liar and fraud."

Rep. Marc Molinaro, R-N.Y., told reporters on his way into a conference meeting this morning, "I can't wait for him to be gone."

Rep. Tony Gonzales, R-Tex., tweeted, "George Santos should be immediately expelled from Congress and a special election initiated at the soonest possible date," while Rep. Steve Womack, R-Ark., told reporters, "This has been going on now since we took the majority. Frankly, I would have hoped along the way that Mr. Santos would have done what I believed was the right thing and not force leadership to force his action, but for him to do it on his own."

The office of Rep. Max Miller, R-Ohio, says his position remains unchanged from the his Jan. 12 statement which said, in part, "I do not believe George Santos can effectively serve and should resign."

In other statements released Tuesday night by Santos' fellow New York Republicans, Rep. Nick LaLota said, "These charges bring us one step closer to never having to talk about this lying loser ever again," while Rep. Mike Lawler said, "I reiterate my call for George Santos to step down" and Rep. Anthony D'Esposito said, "As a retired NYPD Detective, I am confident the justice system will fully reveal Congressman Santos' long history of deceit, and I once again call on this serial fraudster to resign from office."

Other GOP House members from New York who have previously called for Santos to step down include Rep. Nick Langworthy and Rep. Brandon Williams.

Rep. French Hill, R-Ark., told CNN Tuesday night, "I do believe that if a member of Congress is charged with a federal crime they should resign," and Rep. Nancy Mace, R-S.C., told CNN, "We should really hold our own accountable and recruit someone who's going to be better."

-ABC News' Lauren Peller, Gabe Ferris, Katherine Faulders and Jay O'Brien