HARRISBURG, Pa.—The first legal test for Pennsylvania's tough new voter identification law has started, with state lawyers calling the law a completely rational step while opponents attacked it as unnecessary and unjustified.

Lawyers delivered their opening statements Wednesday to Commonwealth Court Judge Robert Simpson, who must decide whether to block the law from taking effect in this year's election as part of a wider challenge to its constitutionality.

The law is the subject of a furious debate over voting rights as Pennsylvania is poised to play a key role in deciding the presidential contest in the Nov. 6 election.

Republicans say it's necessary to prevent fraud. But Democrats say it's an election-year scheme to steal the White House and contend that there's no track record of fraud that it would prevent.