The high court session began Thursday, 54 days before Pennsylvanians help decide who will be president.
The state’s lawyers say lawmakers properly exercised their constitutional latitude to make election-related laws and that every registered voter, including those suing, will be able to cast a ballot.
But lawyers for the plaintiffs insist many registered voters don’t know about the requirement, don’t have a valid ID or will be unable to get one.
The high court is hearing the politically charged case with just six justices: three Democrats and three Republicans. A 3-3 deadlock would allow the law to stand.