The decision by Commonwealth Court Judge Robert Simpson on the law requiring each voter to show a valid photo ID could be appealed to the state Supreme Court.
However, Simpson based his decision on guidelines given to him days ago by the high court justices, and it could easily be the final word on the law just five weeks before the Nov. 6 election.
Simpson ordered the state not to enforce the photo ID requirement in this year's presidential election but will allow it to go into full effect next year.
One lawyer for the plaintiffs said it appeared to be a "win." Election workers will still be allowed to ask voters for a valid photo ID, but people without it can vote on a regular voting machine in the polling place and would not have to cast a provisional ballot or prove their identity to election officials after the election.
His ruling came after listening to two days of testimony about the state's eleventh-hour efforts to make it easier to get a valid photo ID. He also heard about long lines and ill-informed clerks at driver's license centers and identification requirements that made it hard for some registered voters to get a state-issued photo ID.
The 6-month-old law -- now among the nation's toughest -- has sparked a divisive debate over voting rights and become a high-profile political issue in the contest between President Barack Obama, a Democrat, and Republican nominee Mitt Romney, for Pennsylvania's prized 20 electoral votes.
Pennsylvania, traditionally considered one of the most valuable a presidential swing states, is showing a persistent lead for Obama in independent polls. As a result, the state has been virtually empty of presidential TV ads and off the candidates' beaten paths to more contested states in recent weeks.
Pollsters had said Pennsylvania's identification requirement could mean that fewer people ended up voting and, in the past, lower turnouts have benefited Republicans in Pennsylvania.
But Democrats have used their opposition to the law as a rallying cry, turning it into a valuable tool to motivate volunteers and campaign contributions while other opponents of the law, including labor unions, good government groups, the NAACP, AARP and the League of Women Voters, hold voter education drives and protest rallies.
The voter ID law was a signature accomplishment of Pennsylvania's Republican-controlled Legislature and its Republican governor, Tom Corbett. Republicans, long suspicious of ballot-box stuffing in the Democratic bastion of Philadelphia, justified it as a bulwark against any potential election fraud.
Democrats objected furiously, accusing Republicans of using old-fashioned Jim Crow tactics to steal the White House from Obama by making it harder for young adults, the poor, minorities and the disabled to vote.
Protests, warnings of Election Day chaos and voter education drives ensued, as the law's opponents began collecting stories of people who had no valid photo ID and had encountered stiff barriers in their efforts to get one from state driver's license centers.
It was already a political lightning rod when a top state Republican lawmaker boasted to a GOP dinner in June that the ID requirement "is going to allow Gov. Romney to win the state of Pennsylvania."
A wave of new voter identification requirements have been approved in the past couple years, primarily by Republican-controlled Legislatures.
The U.S. Supreme Court upheld Indiana's voter ID law in 2008, and Georgia's top court upheld that state's voter ID law. But a federal court panel struck down Texas' voter ID law, and the state court in Wisconsin has blocked its voter ID laws for now. The Justice Department cleared New Hampshire's voter ID law earlier this year, and a federal court is reviewing South Carolina's law.
The plaintiffs -- a group of registered voters, plus the Homeless Advocacy Project, the League of Women Voters of Pennsylvania and the Pennsylvania chapter of the National Association for the Advancement of Colored People -- had sought to block the law from taking effect in this year's election as part of a wider challenge to its constitutionality.
The constitutionality of the law was not a question before Simpson.
Rather, the state Supreme Court had ordered him to stop the law if he thought anyone eligible would be unable to cast a ballot because of it or if he found the state had not complied with law's promise of providing liberal access to a photo ID that voters were required to carry on Election Day.
Last week, the Corbett administration overhauled the process for getting a voting-only ID card -- an admission that the state had not met the Supreme Court's test for the whether the law should stand.