WASHINGTON—Senate Republicans released an updated version of President Trump’s “big beautiful bill” ahead of plans to start voting as early as later Saturday, but it was unclear whether the mix of changes would be enough to win over holdouts without creating new ones.

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