In what could be a landmark decision, the supreme court of the U.S. state of Pennsylvania has ruled that the state's elimination of zoning and land-use planning rights of local communities to allow oil and gas exploration is unconstitutional.

The decision in late December was in response to a challenge filed by several municipalities against the state legislature's 2012 adoption of the legislation known as Act 13, which removed barriers to the expansion of drilling and fracking across the state.

Earlier, Pennsylvania's Commonwealth Court - the trial court for actions brought against the state - had ruled in favor of the municipal plaintiffs, striking down portions of the act.  However, the decision was subsequently appealed.

In a departure from the lower court's decision and from prior rulings, the state supreme court said its decision was rooted in the state's Environmental Rights Amendment, rather than the property rights of landowners. Its interpretation is that the state cannot interfere with the constitutional duty of municipal governments to enforce the environmental legislation.