Traffic was tied up throughout Chicago's Loop Friday afternoon as the city hosted the largest march of Latinos ever recorded in the country.

Nearly 100,000 demonstrators were said to be in the Loop for a march and rally downtown protesting a proposed law that could send illegal immigrants to jail.

The U.S. flag and banners from Mexico, Honduras and many other countries were flying above thousands of supporters of immigrants rights gathered at federal plaza for the rally.

Rep. Luis Gutierrez told the crowd that immigrants are here to stay. And the Illinois Democrat pledged to work to block a controversial bill that would drastically strengthen immigration laws.

"Shut the Senate down until you get the voice of immigrants who work so hard," said Rep. Luis Gutierrez.

Gov. Rod Blagojevich got a loud cheer from the crowd when the told them in Spanish that immigrants aren't criminals, they're workers. The governor said that he's proud to support immigrant rights.

And Chicago Mayor Richard Daley told the crowd that everyone in America is an immigrant and that no one should turn their backs on new immigrants now.

Speaking from the podium, Daley said, "Do not allow anyone to tell you that you're an immigrant. Everyone in America is an immigrant."

NBC5's Lisa Tutman reported from amidst a huge crowd in Union Park, at Ashland Avenue and Lake Street, where the crowd gathered for hours Friday morning.

They were gathered in strong opposition to a bill they say is clearly anti-immigration.

"HR4437 would criminalize our mothers, our fathers, our daughters (and) our sons that are undocumented," said Julie Santos, of LaFamilia Unida.

Among the protesters was Elizabeth Navarro, who told Tutman she needed to be there and insisted that her 12-year-old twin daughters come, too. She said the proposed immigration reform measure goes too far.

"This country is built on immigrants and, being built on immigrants, why do they now want to discriminate and treat them like criminals?" Navarro said.

The U.S. House of Representatives has already passed the bill, which includes some of the most sweeping changes ever in immigration law.

"Look at it this way," said demonstrator Ramone Hernandez. "If we do the same thing in Mexico and say to all the white people, 'Hey, get out of my country,' you know? We're not criminals. We just come here to work. That's all we do."

According to provisions in HR4437, unlawful presence in the U.S. would be considered a felony, with undocumented immigrants facing potential jail time.

Also, anyone who knowingly assists an undocumented immigrant could also face criminal charges. That, in particular, doesn't sit well with Dr. Sean Gavin, a chiropractor whose treatment of undocumented immigrants could land him in jail, as well.

"Myself, as a doctor, if I am to attend to my patients, I would be under a felony under 4437, because I'm tending to people. I'm helping and aiding and abetting illegal aliens here. So this is a bill that has to stop," Gavin said.

Tutman said that despite the huge opposition to the measure, which now heads to the U.S. Senate for a vote, there are many groups that fully support the propsed reform, saying that without it, the country only compounds the growing problem of illegal immigration.

"It really bothers me that I see a lot of Latinos now standing up to break the law," said Rosanna Pulido, of the Illinois Minutemen Project. "It's shameful to me."

The demonstrators began marching from Union Park at about noon, moving to the federal plaza where a massive rally began at about 2 p.m.

Crowds were still pouring into the plaza after 3 p.m. and participants said they are hoping that their message and their numbers will influence the upcoming Senate vote.

Commuter Alert

In the wake of the demonstration Friday, the following CTA buses were being rerouted, according to CTA spokeswoman Ibis Antongiorgi: No. 7 Harrison; No. 8 Halsted; No. 9 Ashland; No. 20 Madison; No. 22 Clark; No. 24 Wentworth; No. 36 Broadway; No. 60 Blue Island; No. 62 Archer; No. 124 Navy Pier; No. 126 Jackson; No. 151 Sheridan; No. 156 La Salle; No. 157 Streeterville.

Just before 3 p.m., the No. 9 Ashland bus and No. 20 Madison were back to their normal routes, Antongiorgi said. The rerouting, in anticipation of the rally, began about 1 p.m. as the rally proceeded into the Loop, she said.

As of about 2:45 p.m., the following streets were closed, according to police News Affairs: Clark Street from Michigan Avenue to Jackson Street, Canal Street between Van Buren and Washington Streets, Adams Street between Michigan Avenue and Clark Street and Jackson Boulevard from Ashland Avenue to Franklin Street.

CTA was also warning customers to allow for extra travel time due to heavy ridership on the rail lines.