Senate parliamentarian Elizabeth MacDonough has rejected the third and most recent plan from Democrats for including immigration reform in the Build Back Better bill, telling senators that it doesn't meet the rules for what can be included in a budget measure bypassing the Senate's filibuster.

The guidance is the latest setback for Democrats' hopes of including immigration reform in the spending bill. MacDonough had previously rejected two plans from Democrats that would have provided a pathway to citizenship for millions of immigrants.

The third plan stopped short of that, aggravating some activists and progressives. It would have granted 6.5 million foreign nationals a temporary parole status that would give them five-year work and travel permits.

Sen. Dick Durbin (D-Ill.), who chairs the Judiciary Committee, said he was "disappointed" and that Democrats are "considering what options are available."

What comes next isn't clear. Durbin huddled with Senate Majority Leader Charles Schumer (D-N.Y.) and Sen. Bob Menendez (D-N.J.), who has been involved in the immigration discussions, shortly after news of MacDonough's ruling broke.

“We strongly disagree with the Senate parliamentarian’s interpretation of our immigration proposal, and we will pursue every means to achieve a path to citizenship in the Build Back Better Act,” they said in a joint statement with Sens. Catherine Cortez Masto (D-Nev.), Ben Ray Luján (D-N.M.) and Alex Padilla (D-Calif.).

Asked if there was a "Plan D," Durbin told reporters: "Not at this point."

Democrats pitched MacDonough, who is undergoing treatment for breast cancer, on the latest plan roughly two weeks ago, but said as recently as this week that they had gotten little signal from her on which way she was leaning on their latest plan.

The ruling isn't binding and immediately fueled calls for Democrats to try to sidestep the parliamentarian's guidance.

"It’s time for Senate leaders to retake control of the legislative process. ... The Senate has received some bad advice that needs to be disregarded," said American Business Immigration Coalition co-chair Mike Fernandez. 

Some Democrats, including Durbin, support trying to formally overrule MacDonough. But that would require 50 votes and would ultimately fall short given opposition from Sens. Joe Manchin (D-W.Va.) and Kyrsten Sinema (D-Ariz.).

Advocates are instead urging Democrats to try to put someone in the chair that would ignore MacDonough's advice, though that wouldn't prevent Republicans from trying to win over one Democrat to strip out the plan as part of a chaotic floor process where any senator who wants to force a vote on a change to Biden's spending bill will be able to. 

Democrats initially pitched MacDonough on using their spending bill to provide 8 million green cards to immigrants in four groups: "Dreamers," who came to the U.S. illegally as children; temporary protected status holders; agricultural workers and other essential workers. But she rejected that earlier this month, saying that it was "not appropriate" for reconciliation, the budget process Democrats are using to bypass the filibuster on their spending bill.  

MacDonough warned Democrats that their second plan — to change to the registry date for certain undocumented immigrants and beneficiaries of humanitarian parole programs — faced a similar setback. 

Asked why MacDonough nixed their latest plan, Durbin indicated that they had hit the same roadblock. 

"Same reasoning, just too many rights extended," Durbin said, before declining to characterize MacDonough's guidance further. 

The parliamentarian's guidance stated that Democrats' third immigration proposal "is not much different in its effect than the previous proposals we have considered." 

"These are substantial policy changes with lasting effects just like those we previously considered and outweigh the budgetary impact," the guidance, a copy of which was obtained by The Hill, adds. 

Republicans, who argued against the immigration plan, immediately declared victory. Sen. Chuck Grassley (Iowa), the top Republican on the Judiciary Committee, said the parliamentarian's guidance was "just an affirmation of the obvious."

“Passing these measures on a party-line vote would set a terrible precedent and further erode the valuable role of the Senate as a legislative body that requires debate, consultation, and compromise in order to enact major policy proposals into law," he said.

Rafael Bernal contributed.

Updated at 8:14 p.m.