The opponents' strategy: to trot in voter after voter, many of them elderly, to tell their own stories about how difficult, if not impossible, it will be for them to get the required forms of ID in time to vote on Nov. 6.
Though the courthouse is just down the street from the Capitol, the dispute will fuel a national debate over whether a recent wave of strict voter-ID laws in many states is a partisan effort to keep certain voters home and sway elections.
"All eyes are on Pennsylvania," said Wendy Weiser, who directs the Democracy Program at New York University's Brennan Center for Justice, where voting issues are studied. "It is clearly a significant swing state, and the outcome of this case might very well have a significant impact on the outcome of the election."
ACLU lawyers, who declined to be interviewed Tuesday about the case, have asserted in legal briefs that "the real purpose of the photo ID law is not ensuring the integrity of the electoral process, but ensuring political advantage through the exclusion of qualified voters who are perceived supporters of the opposition."
The ACLU is suing on behalf of 10 Pennsylvanians who do not have driver's licenses and who contend that the photo-ID requirement violates the state constitution, depriving them of their right to vote.
In legal papers filed last week, the civil liberties group says that those 10 are the tip of a human iceberg, that as many as a million or more Pennsylvania voters lack the types of photo ID that the law requires.
The ACLU included in its filing a surprising concession from state officials: a written stipulation that the state cannot pinpoint any instance of the kind of voter-impersonation fraud the new law aims to prevent.
The state stipulated that it is "not aware of any incidents of in-person voter fraud in Pennsylvania," and has "no direct knowledge of in-person voter fraud elsewhere." State officials also said they would offer no evidence that "in-person voter fraud is likely to occur in November 2012 in the absence of the photo ID law."
The state Attorney General's Office, which is defending the Corbett administration against the suit, declined to discuss the case Tuesday. But in a response filed last week, Senior Deputy Attorney General Patrick Cawley said the legislature had the authority and wide discretion to regulate voting and argued that the law would disenfranchise no one.
The 10 plaintiffs, Cawley said, will have ample opportunity between now and Nov. 6 to obtain acceptable identification.
Under the law, various forms of photo identification will be accepted, including valid U.S. passports, college student identification cards with expiration dates, current military identification, and ID cards issued to government employees.
For those without any of the above, the Pennsylvania Department of Transportation will issue non-drivers' photo identification cards free to those who apply and bring other proofs of identity.
And amid complaints that some residents - especially those who are elderly or disabled - would have to spend time and money digging up documents such as birth certificates, the state last week came up with a new plan: a special Department of State voting card that would require less paperwork to obtain. The card, to be made available next month, could only be used for voting.
In court Wednesday, the state is expected to argue that obtaining a state-issued card is not burdensome, and that applicants can turn to family members and friends for help getting to a PennDot center to obtain one.
Still, Secretary of the Commonwealth Carol Aichele acknowledged Tuesday at a news conference in the Capitol that transportation for such voters remained "an issue."
Aichele said she was confident that the state's efforts to provide voters with suitable ID, coupled with an aggressive campaign to educate voters on the new law, would help ensure that voters could cast their ballots without problems.
"We do not plan on having any hangups in this election," she said.
One big question is how many people will face problems obtaining a state-issued photo ID. When Republican legislators were pushing the bill into law, the Corbett administration estimated that 99 percent of the state's voters already had the photo identification necessary to vote in November.
That estimate was later torpedoed by the Department of State, which announced this month that as many as 9.2 percent of the state's 8.2 million voters lacked driver's licenses or non-drivers' photo IDs.
The state cautioned at the time that those numbers were likely inflated for a number of reasons, among them that they included thousands of inactive voters - people who had not voted for more than four years and likely had moved from Pennsylvania.
Aichele, at her news conference, would provide no new estimates of how many people might be affected by the new law.
But that question is bound to be a key part of legal arguments in the hearing in the ACLU case, which is expected to last seven days.
The case is being heard by Robert "Robin" Simpson, a former Northampton County judge who was praised by the state bar as smart, courteous, and fair when he was first elected in 2001 to Commonwealth Court, the appellate bench that hears government agency disputes.
Whether the ID law so burdens some voters as to infringe on their voting rights, or is within the state's power to run and regulate elections, is for Simpson to decide. But no one expects the fight to end there. One side or the other is sure to try to appeal to the state Supreme Court.
All that is separate from the U.S. Justice Department's Monday request that the state turn over records so federal civil-rights lawyers can determine if the new law complies with the Voting Rights Act of 1965, which bars election laws that discriminate on the basis of race.
So, plenty of legal and political debate may follow before it is known if the Rev. Benjamin T. Hailey Sr., president of the Pennsylvania Baptist State Convention, accurately described the law at Tuesday's protest rally in Harrisburg.
"In Philadelphia, there is a bell with a crack," Hailey said. "This law cracks the liberty of every citizen of this commonwealth."
Contact Angela Couloumbis at 717-787-5934 or firstname.lastname@example.org, or follow on Twitter @AngelasInk.
Inquirer staff writer Clara Ritger contributed to this article.