The justices ruled that a set of changes made to Megan's Law in 2004 was not constitutional, noting that the legislation also included such measures as a two-year statute of limitations on asbestos actions, the jurisdictional parameters of park police, and revisions to real estate law.

The court then put its decision on hold for three months to allow the Legislature to find a remedy.

"We will stay our decision, as we have done under similar circumstances, in order to provide a reasonable amount of time for the General Assembly to consider appropriate remedial remedies, and to allow for a smooth transition period," wrote Justice Debra Todd for the five-justice majority.

As revised in 2004, Megan's law created a searchable online database of offenders, set new punishments for offenders who did not register, and added luring and institutional sexual assault to the list of offenses that require 10-year registration.

It also set notification rules for out-of-state offenders who move to Pennsylvania, altered duties of the Sexual Offenders Assessment Board, and established community notification about sexually violent offenders.

Todd said the single-subject rule, which dates to 1864 and has recently been a factor in several high-profile cases, gives people confidence they can weigh in before a bill is passed, and helps lawmakers know what they are voting on ahead of time.

"When an act of the Legislature violates the single-subject rule, all of its provisions are equally repugnant to the constitution, and, thus, equally void," Todd said.

Chief Justice Ronald Castille filed a lone dissent, saying it was a close question but that he would have upheld the law.

"Any law passing through the enactment process is the result of salutary legislative compromise and the single-subject rule is not intended to completely discourage such compromise," Castille wrote.