The Senate parliamentarian on Wednesday ruled against Democrats’ plan to legalize undocumented immigrants by updating a decades-old immigration registry, the latest blow to lawmakers’ efforts to include major immigration changes in their reconciliation package.

The decision is a major setback for Democrats, who have promised to overhaul the immigration system as part of their sweeping $3.5 trillion budget reconciliation bill to remake American social programs.

Following her meeting Wednesday with Senate Democrats, Parliamentarian Elizabeth MacDonough rejected plans to update the immigration registry through reconciliation, according to a Senate aide.

MacDonough told lawmakers that updating the registry would be a “weighty policy change,” according to materials obtained by CQ Roll Call. She hinted that any bill adjusting the status of millions of undocumented immigrants would not pass muster under Senate rules for budget reconciliation bills.

“The change in status to LPR [lawful permanent residency] remains a life-long change in circumstances the value of which vastly outweighs its budgetary impact,” she said.

Sen. Richard J. Durbin, D-Ill., expressed “disappointment” with the decision and said alternative options were “limited.”

“As people live desperate lives for fear of a knock on the door and no future for the kids, unfortunately we can’t find the language to clear for the reconciliation that might help them,” Durbin said. “But yeah, we’re gonna keep trying.”

Earlier this month, the parliamentarian rejected Democrats’ original plan to create a pathway to citizenship for immigrants brought to the U.S. as children, essential workers, and people fleeing countries in crisis.

[Senate parliamentarian rejects Democrats’ immigration bid]

After that initial ruling, lawmakers vowed to try again with a different plan. The budget reconciliation package, which can pass with a simple majority, is likely Democrats’ best chance for the foreseeable future to make any headway on immigration policy.

The alternative plan reviewed this week would have involved moving up the date on the immigration registry, an existing law currently set at 1972, allowing immigrants who have resided in the U.S. since then and who have demonstrated “good moral character” to become permanent residents.

Last week, Sen. Bob Menendez, D-N.J., said he would “personally prefer” this option since it would involve an update, not a change, to the law, which could be more palatable to the nonpartisan parliamentarian.

But the pressure to make some sort of progress is high. Immigration advocates, frustrated after years of partisan stalemate, have urged Democrats to overrule the parliamentarian or nix the Senate filibuster altogether to secure a pathway to citizenship before they potentially lose their congressional majorities next year.

Three House Democrats have threatened to vote against the package unless it includes immigration provisions, nearly enough to sink the bill if Republicans are united in opposition.

The battle over which immigration provisions are permitted is far from the only challenge facing the reconciliation package.

Speaker Nancy Pelosi has promised a Thursday vote on the bipartisan infrastructure bill, but progressives have said they will vote it down unless more progress is made on the reconciliation package. Key Senate moderates have not yet clarified what they will and will not support in that package.

Suzanne Monyak, Jennifer Shutt and Niels Lesniewski contributed to this report.