WASHINGTON—Former White House cost-cutting czar Elon Musk called President Trump’s “big, beautiful” tax-and-spending package a “disgusting abomination,” stepping up his criticism just as the Senate is trying to quickly pass the measure and get it signed into law by July 4.

"Shame on those who voted for it: you know you did wrong," the Tesla CEO wrote, citing projections that the legislation would add more than $2 trillion to the national debt.