Pennsylvania's Supreme Court is asking a lower court to take a closer look at a controversial voter identification law, the latest twist in a dispute over voting rights in the election swing state.

The new law tightens requirements about what types of identification Pennsylvanians can present before being allowed to vote: whereas before Pennsylvania residents could use non-photographic documents like a utility bill, now they must have goverment-sanctioned photo IDs. Critics say the law will disenfranchise poor and minority voters, who are less likely to have proper identification.

A Pennsylvania judge upheld the law in August, leading plaintiffs to appeal to the state's highest court. In a 4-2 vote on Tuesday, the Pennsylvania Supreme Court ordered the lower Commonwealth Court to determine whether voters have trouble getting the required identification.

If the lower court finds that the process of obtaining a new ID isn't too much of a burden, the Supreme Court said, the voting law should stand. But if it is prohibitively difficult to get identification -- in other words, if the risk of Pennsylvanians being unable to vote is too high -- the Supreme Court said the law should be struck down.

"Both state agencies involved appreciate that some registered voters have been and will be unable to comply with the requirements," the court decision reads, noting that voters are generally required to present a birth certificate, social security card and two additional forms of documentation proving Pennsylvania residence.

Noting that "the population involved includes members of some of the most vulnerable segments of our society (the elderly, disabled members of our community, and the financially disadvantaged)," the court warned of "a disconnect between what the Law prescribes and how it is being implemented."

If the Commonwealth Court finds sufficient risk of disenfranchisement, the decision says, it is "obliged to enter a preliminary injunction" blocking the voter ID requirement from taking effect.

The legal challenge has taken on immense significance given Pennsylvania's pivotal role as a battleground state in presidential elections. While Mitt Romney's campaign has quietly sent signals that the state may be out of reach, independent groups favoring Romney have spent heavily there in hopes of securing its 20 electoral votes.

Similar battles have played out state by state across the country, pitting proponents of new laws allegedly designed to prevent fraud at the polls against voting rights advocates who warn of a concerted attempt to suppress certain groups of voters.