Voter support for President Barack Obama's healthcare overhaul rose after the US Supreme Court upheld it but most people still oppose the law, according to a Reuters/Ipsos poll on Sunday.

The online survey showed increased backing from Republicans and, crucially, the political independents whose support will be essential to winning the Nov 6 presidential election.

Thirty-eight percent of independents support the healthcare overhaul in the poll conducted after the court ruled on Thursday the law was constitutional. That was up from 27 percent from a Reuters/Ipsos poll taken days before the justices' ruling.