WASHINGTON (AP) — The Senate parliamentarian has advised that a key Medicaid provider tax overhaul that is central to President Donald Trump's big tax cut and spending bill does not adhere to procedural rules, delivering a crucial blow to Republicans rushing to finish the massive package this week.

The guidance Thursday from the parliamentarian is rarely ignored, and it forces GOP leaders to consider options. Senate leaders could try to revise or strip it from the package. Otherwise, the provision could be challenged during floor votes, requiring a 60-vote threshold to keep it, a tall order in the narrowly split Senate. Democrats are unified against the Republican president’s bill.

Republican leaders are relying on the provider tax change to save billions of dollars from the Medicaid health care program for the massive tax cuts package. But they had been struggling to rally support because several GOP senators warn it would harm rural hospitals who depend on the funds.

The outcome is a setback as Senate Republicans hoped to launch votes on the package by the end of the week, to meet Trump’s Fourth of July deadline for passage.