The Senate parliamentarian has advised that a Medicaid provider tax overhaul central to President Donald Trump’s tax cut and spending bill does not adhere to the chamber’s procedural rules, delivering a crucial blow as Republicans rush to finish the package this week.

Guidance from the parliamentarian is rarely ignored and Republican leaders are now forced to consider difficult options. Republicans were counting on big cuts to Medicaid and other programs to offset trillions of dollars in Trump tax breaks, their top priority. Additionally, the Senate’s chief arbiter of its often complicated rules had advised against various GOP provisions barring certain immigrants from health care programs.

Republicans scrambled Thursday to respond, with some calling for challenging, or firing, the nonpartisan parliamentarian, who has been on the job since 2012. Democrats said the decisions would devastate GOP plans.

“We have contingency plans,” said Majority Leader John Thune of South Dakota.