A handful of Republican-controlled states have vowed to challenge President Barack Obama’s US healthcare reforms in court.
Thirty-two million more Americans will be covered under the changes, which were passed by just seven votes early on Monday morning.
The bill was a key platform of Obama’s domestic policy on the campaign trail to the White House.
But attorney-generals in 12 Republican states say it is unconstitutional as they claim it infringes on their powers.
Critics of the reforms argue the changes will only drive up costs.
Obama’s healthcare bill levies new taxes on the wealthy and bans insurance companies from refusing to cover those with pre-existing conditions.
The president is set to sign the bill into law on Tuesday.