Senate Republicans are racing to pass a budget bill that is pivotal to President Donald Trump's second-term agenda ahead of a self-imposed 4 July deadline.
Party leadership have been twisting arms for an initial vote on the "Big Beautiful Bill" on Saturday, following the release of its latest version - all 940 pages - shortly after midnight.
Rank-and-file Republicans have been divided over how much to cut from welfare programmes in order to cover the cost of extending some $3.8tn (£2.8tn) in Trump tax breaks.
The sprawling tax and spending measure passed the House of Representatives by a single vote last month.