The "American Dream and Promise Act" would create a path to citizenship and permanent legal status for millions of undocumented immigrants.
Proponents say it would benefit the so-called Dreamers, people with temporary protected status, and those under Deferred Enforced Departure.
Pelosi quoted President Ronald Reagan, saying, "If we ever close the door to new Americans, our leadership in the world would be lost."
Watch: Pelosi, de Blasio push for immigration reform
The bill would extend protection for Dreamers who have been in the U.S. for at least four years and would also extend Temporary Protected Status for several million people.
One immigrant from Honduras broke down in tears at the event. Perla Canales said she worries constantly that she might be deported.
"This is my home, and I have a good job," she said.
De Blasio promised to do what he could to protect immigrants.
"While we are waiting for change in Washington, we have your back in New York City," he said. "We will protect you."
The bill's problem is that while it will likely pass in the House, it is destined to die in the Republican-controlled Senate. Additionally, President Donald Trump would likely veto the bill eve if it did pass both the House and Senate.
Still, advocates are pushing for the measure to be passed right away.
Co-authored by Rep. Nydia Velazquez (D-NY), HR6 was introduced in the House of Representatives last week.
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