The Senate Parliamentarian ruled against attaching the measure to a $3.5 trillion spending bill on Sunday, putting a major stumbling block in Senate Democrats’ efforts to allow millions of immigrants to legally stay in the United States, lawmakers said.

The provision aimed to provide a path to citizenship for millions of people, including so-called Dreamer immigrants who were brought to the United States as children and are currently protected from deportation under the Deferred Action for Childhood Arrivals (DACA) program.

Farmworkers, essential workers, and immigrants with temporary protected status, which provides work permits and deportation relief to those from countries ravaged by violence or natural disasters, were also among those who stood to benefit.

Senate Democratic Leader Chuck Schumer said in a statement that Democrats were “deeply disappointed in this decision,” but that “the fight to provide lawful status for immigrants in budget reconciliation continues.”

Senate Democrats have prepared alternative proposals and intend to meet with the Senate parliamentarian again, according to Schumer. A legislative solution has become even more urgent in the aftermath of a July court ruling that invalidated DACA, which now protects approximately 640,000 young immigrants.

A White House spokesperson called Sunday’s ruling “deeply disappointing,” but added, “We fully expect our partners in the Senate to come back with alternative immigration-related proposals for the parliamentarian to consider.”

Senator Chuck Grassley, the top Republican on the Judiciary Committee, praised the parliamentarian’s decision on Twitter, saying, “Mass amnesty for millions of illegal immigrants isn’t a budgetary issue appropriate for reconciliation.”

“Democrats will not be able to stuff their most radical amnesty proposals into the reckless taxing and spending spree they are assembling behind closed doors,” Senate Republican Leader Mitch McConnell said.

According to an estimate in Senate Parliamentarian Elizabeth MacDonough’s ruling obtained by Reuters, the step would have assisted approximately 8 million people in becoming lawful permanent residents, including approximately 7 million who are now deemed to be in violation of the law.

According to MacDonough, if the reform is allowed to proceed in a budget bill, a future Senate could revoke anyone’s immigration status based on a majority vote.

This would be a “stunning development… and is further evidence that the policy changes of this proposal far outweigh the budgetary impact,” she said.

“It is ineligible for inclusion in reconciliation.”

According to MacDonough, lawful permanent status allows people to work, travel, and live openly in American society while eventually becoming eligible to apply for citizenship.

As the Senate’s parliamentarian, MacDonough, who has held the position under both Republicans and Democrats since 2012, advises lawmakers on what is permissible under the chamber’s rules and precedents, sometimes with long-term consequences. The holder of the position will be chosen by the Senate majority leader and is expected to be nonpartisan.

MacDonough barred the inclusion of a minimum wage increase in a COVID-19 aid bill earlier this year.

To be considered for a vote in the United States Senate, most bills must be supported by 60 of the 100 senators. Budget reconciliation measures, on the other hand, can pass with a simple majority vote, in which case Vice President Kamala Harris can break the tie.

According to MacDonough’s ruling, the proposed designation of essential workers covered 18 major categories and more than 220 sub-categories of employment. DACA recipients receive work authorization, access to driver’s licenses, and, for some, improved access to financial aid for education, but no path to citizenship.

The law primarily protects young Hispanic adults born in Mexico and other Central and South American countries who were brought to the United States as children.