HARRISBURG, Pa. (AP) – About one-third of Pennsylvania's 8.3 million voters are unaware of the new state photo ID law that takes effect on Election Day and at least 1 million voters lack the documents they need to take to the polls for their votes to count, lawyers challenging the law said Wednesday.

The American Civil Liberties Union of Pennsylvania and its partners in a lawsuit seeking to block enforcement of the law made the claim in a pretrial brief filed in preparation for a hearing in Commonwealth Court scheduled to begin July 25.

Gov. Tom Corbett's administration originally estimated 1 percent of voters lacked a state-issued ID that would satisfy the law. But earlier this month it released the results of a cross-check of registered voters and PennDOT records that suggested as much as 9 percent lacked licenses or ID cards issued by the Pennsylvania Department of Transportation.

The ACLU estimate comes to 12 percent, and the group's lawyers said the administration estimate was understated because it excluded certain voters, including about 500,000 who have an expired driver's license or non-driver PennDOT ID cards that will not be accepted at the polls.

"The universe of registered voters who lack a valid PennDOT ID is close to 1.4 million voters, according to the commonwealth's own records," the brief says.

The 10 registered voters challenging the law maintain it violates the constitution and represents an attempt to disenfranchise poor people, elderly residents and minorities who may be more likely to vote for Democrats.

In their legal brief Wednesday, state lawyers defended the constitutionality of the law and argued that the plaintiffs lack grounds for a court order suspending enforcement for this year's election, which includes races for offices ranging from the presidency to the Legislature.

"There is ample time before the next election in which interested and eligible voters can obtain a photo ID. The executive agencies of the commonwealth have taken significant steps to remove any barrier to obtaining photo ID," the state legal team said in its brief.

The ACLU brief also revealed that state officials are considering developing a new Department of State ID card partly because of difficulties that people born in other states or countries face in trying to obtain birth certificates. But no decision had been made on whether to proceed, they said.

"The commonwealth's latest concessions confirm what petitioners have said all along – that they and others like them are having a very difficult time obtaining ID that complies with the photo ID law," the brief says.

Calls seeking comment from the governor's office and the State Department were not returned Wednesday.

The Republican governor and his GOP legislative allies, who developed the law and pushed it to his desk without any Democratic votes, contend that the new requirement is a common-sense precaution against voter fraud.