The bipartisan "Gang of Eight" is to introduce the bill Tuesday and a Judiciary Committee hearing now is scheduled for Friday, The Hill reported.
The panel originally was to hear the bill Wednesday.
A spokesman for Sen. Marco Rubio, R-Fla., one of four Republicans working on the legislation with four Democratic counterparts, said the delay was to give senators more time to read the bill.
"The news suggests the immigration bill to be introduced on Tuesday could be lengthy and complex," Rubio aide Alex Conant said.
On his Twitter page, Conant said, "BREAKING: Lots of concern there wouldn't be enough time to read bill before Wednesday's Judiciary hearing, so hearing's been moved to Friday."
The bill will include provisions on tighter border security and will offer a pathway to citizenship for undocumented workers already in the United States, providing they meet a stringent set of requirements.
The pathway has prompted criticism from conservatives who argue no "amnesty" should be granted to people in the country illegally.
Earlier, a person familiar with discussions told The New York Times unauthorized immigrants may have to pay $2,000 as part of the bipartisan immigration reform plan.
The fee, whose amount was not finalized but which would have to be paid before an immigrant could earn legal status, would include $500 when the person applies for a temporary work permit and at least $1,500 that could be paid over 10 years before applying for a green card, the source said.
A Senate aide described the figure as "significant but not impossible, punitive but not unreasonable."
Democrats and immigration advocates had earlier pushed for a lower amount.
The fees, reported Monday, came a day after Rubio, who delivered a keynote address during the Republican National Convention, hit the Sunday TV talk show circuit to dismissed colleagues' fears the overhaul's provisions on citizenship would amount to amnesty.
"It's not amnesty because you pay serious consequences for having violated the law," the first-term senator and possible 2016 presidential contender told NBC's "Meet the Press."
The measure would boost the number of taxpaying Americans and be a "net positive for the country economically, now and in the future," Rubio told "Fox News Sunday" in one of seven Sunday talk show interviews he did on the five major networks, plus the Spanish-language Telemundo and Univision networks.
The measure calls for unauthorized immigrants who arrived in the United States on or before Dec. 31, 2011, to be allowed almost immediately to apply for temporary legal status that would let them live and work in the country.
At the same time, the Department of Homeland Security would be required to monitor the nation's entire Southwest border with Mexico -- and catch 90 percent of people trying to cross the border illegally, Rubio said.
"We are going to get the toughest enforcement measures in the history of this country," he told ABC's "This Week."