The Senate referee who will decide if a $3.5 trillion spending plan can include long-stalled immigration reform is pushing Democrats for more details on their plan as she weighs whether to give it the green light.

Sen. Dick Durbin (Ill.), the No. 2 Senate Democrat and Senate Judiciary Committee chairman, said Monday that Democratic staffers will present parliamentarian Elizabeth MacDonough with new information this week after they initially briefed her Friday on their reasoning for including immigration reform in the spending bill. 

"She still has to make the decision. She asked for additional information, which we're presenting this week," Durbin said, adding that it would be related to the "legal theories."

"We feel very strong about that position, and we hope it is persuasive, but ultimately it is her decision," Durbin continued.

Senate Democrats want to include a plan that would give 8 million green cards to four groups: "Dreamers," temporary protected status holders, and agricultural and essential workers. If an immigrant is granted legal permanent resident status, that paves the way for them to eventually apply for citizenship if they can meet other qualifications.

Because Democrats are using reconciliation to try to pass the $3.5 trillion spending plan without GOP votes, the bill has to comply with arcane rules that govern what can be included. The most well-known requirement is that the immigration plan has an impact on federal spending and revenue and that its impact isn’t “merely incidental” to its nonbudgetary goals.

Durbin said that Democratic staffers felt "good about" their presentation.

"I hope they are right," he said.

The spending bill represents the best shot for Democrats to get immigration reform to Biden's desk after years of setbacks. Durbin has also been leading a bipartisan group to try to come up with a bill that could get 60 votes, the number needed to defeat a filibuster, but it has yielded little success.

If MacDonough says that it doesn't comply with the budget rules, the immigration plan either will have to be stripped out or Democrats will need to muster 60 votes to keep it in.

Republican staffers also made their pitch to MacDonough on Friday about why the immigration plan shouldn't be included.

"My staff is very much involved in it. ... We're at the table," Sen. Chuck Grassley (Iowa), the top Republican on the Judiciary Committee, said on Monday, adding that there were "ongoing discussions."

Senate Majority Leader Charles Schumer (D-N.Y.) has set a self-imposed deadline of Wednesday for Senate committees to be done drafting their parts of the bill.

But Durbin indicated that the Judiciary Committee could miss that deadline because it won't have a final draft of its piece of the spending package until it gets a decision by the parliamentarian on the immigration plan.

"The language coming out of our Judiciary Committee is being vetted through the parliamentarian's office, so we are not prepared to do any final draft until we get that work done," he said.