There will never be a time when every voter will be able to comply with the law, said Justice J. Michael Eakin, a Republican.
Gersch had earlier told the court that there would be no need for a lawsuit if the state would provide every voter with a compliant ID.
"That will never happen," Eakin said. "There will always be someone burdened by it."
Reading from the Pennsylvania Constitution, Article 7, Section 1, which sets out the basic qualifications for voters in the state, Todd said of the voter ID law that "it does appear to be completely contrary to the language of our constitution."
Knorr pointed out that, until now, voters identified themselves by signing in at their polling places. "This is not different in kind from that," he said.
"But it's a new burden," Todd said.
"Sure, but it's minimal," Knorr answered, to laughter from the packed courtroom.
The ACLU is expecting a decision from the Supreme Court by the end of the month, said spokeswoman Sara Mullen.
Commonwealth Court Judge Robert Simpson ruled last month that the law doesn't violate the state's constitution on its face.
While Simpson found "disturbing" the often quoted statement by House Republican Majority Leader Mike Turzai that passage of the voter ID law "is going to allow [former Massachusetts] Governor [Mitt] Romney to win the state of Pennsylvania," he said that it didn't invalidate the legislature's legitimate interest in preserving the public's confidence in elections by discouraging in-person voter fraud through the use of photo IDs.
Also hearing the case were Justice Max Baer, a Democrat, and Chief Justice Ronald D. Castille, a Republican. Justice Joan Orie Melvin, also a Republican, could not sit for the case because she is under suspension pending criminal charges in the Allegheny County Court of Common Pleas.