The Supreme Court ruled narrowly Monday in a challenge to the landmark Voting Rights Act, exempting a small Texas governing authority from a key provision of the civil rights law but side-stepping the larger constitutional issue.

The court, with only one justice in dissent, avoided the major constitutional questions raised in the case over the federal government's most powerful tool to prevent discriminatory voting changes since the mid-1960s.

The law requires all or parts of 16 states, mainly in the South, with a history of discrimination in voting to get approval in advance of making changes in the way elections are conducted.

The court said that the Northwest Austin Municipal Utility District No. 1 in Austin, Texas, can opt out of the advance approval requirement, reversing a lower federal court that found it could not.

Chief Justice John Roberts, writing for the court, said the larger issue of whether dramatic civil rights gains means the advance approval requirement is no longer necessary "is a difficult constitutional question we do not answer today."

The court's avoidance of the larger issue explains the consensus among justices in the case rendered Monday, where they otherwise likely would have split along conservative-liberal lines.

Justice Clarence Thomas, alone among this colleagues, said he would have resolved the case and held that the provision, known as Section 5, is unconstitutional.

"The violence, intimidation and subterfuge that led Congress to pass Section 5 and this court to uphold it no longer remains," Thomas said.