A radical immigration overhaul to be proposed this week by President-elect Joe Biden would include a path to citizenship that could see millions of illegal immigrants become U.S. citizens in just eight years.

Vice President-elect Kamala Harris told Univision last week that the immigration bill would be "first order of business" and will be about "creating a pathway for people to earn citizenship." She said that pathway would be eight years long.

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The Washington Post reported Monday that the bill, to be unveiled on Inauguration Day Wednesday, would put illegal immigrants into protected status and a five-year pathway to a green card. If they meet certain conditions, such as payment of taxes and a background check, they could then be put on a three-year pathway to citizenship. Some estimates put the population of illegal immigrants at around 12 million as of 2015, other estimates are higher. 

The Associated Press, which also reported that the eight-year path is in the bill, noted that it would be one of the fastest pathways to citizenship for illegal immigrants in recent years.

A pathway to citizenship -- not just legal status -- for illegal immigrants has been a top agenda item for liberals and immigration activists for decades and now -- with Democratic control of the White House, House and Senate -- that goal could be in sight.

It would also grant immediate green cards to hundreds of thousands of illegal immigrants protected from deportation under Temporary Protected Status (TPS) and Deferred Action for Childhood Arrivals (DACA) programs. President Trump had moved to abolish DACA, the 2012 Obama-era executive order that protected those who came to the U.S. as children. But he was rebuffed by the Supreme Court, and Harris said that "we are going to expand protections for Dreamers and DACA recipients."

"These are some of the things that we're going to do on our immigration bill. And we believe it is smarter and a more humane way of approaching immigration for immigrants," she said.

The Post reported that the bill would also include border security provisions at the border, and said it would see increased technology at the border -- but it is unclear what this involves. Biden has promised that "not another foot" of President Trump’s border wall will be built under his administration.

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The bill would also include provisions to stem the flow of migration by addressing root causes of migration from south of the border. Biden had, during the campaign, promised a $4 billion four-year plan of assistance to be linked with reforms from those countries.

On legal immigration, the Post reported that the bill would open a number of further avenues of legal immigration -- including "recapturing" unused visas from prior years, giving work permits to the spouses and children of temporary visa holders.

While the bill has a good chance of being passed in the Democrat-controlled House, it is unclear of its chances in the Senate. It would need 60 votes to pass the chamber, meaning 10 Republicans would have to vote in favor. A number of past efforts at immigration reform have failed, including a 2013 effort under President Barack Obama.

While Republicans have indicated they are open to working with Biden on his key legislative priorities, GOP lawmakers have traditionally demanded that any amnesty of illegal immigrants be accompanied by muscular enforcement at the border. Republicans are likely to face pressure from its conservative base opposed to legalizing millions of illegal immigrants.

The legislation is one of a number of radical actions on immigration that Biden has promised to take. He has promised to implement a moratorium on deportations and to end a number of Trump-era programs to stop illegal immigration, including the Migrant Protection Protocols. He has also pledged to dramatically increase the number of refugees the U.S. takes in every year.

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Meanwhile, the Biden administration will face an early challenge in the form of a caravan of thousands of migrants moving toward the border from Honduras. That caravan has called on the administration to honor its "commitments" to them.

But, in a possible nod to fears of a migrant surge at the border with a new bill, the Post reported that the pathway to citizenship would only apply to those who arrived in the country before Jan. 1.

Fox News' Jacqui Heinrich and The Associated Press contributed to this report.