The Pennsylvania Supreme Court on Tuesday issued an opinion that upholds and further develops an environmental rights amendment in the state's constitution that fossil fuel opponents have increasingly invoked in legal challenges to hinder shale gas development.

The justices reversed and vacated a 2015 opinion by the Commonwealth Court that found Pennsylvania could issue oil and gas leases for state-owned land and use that revenue for the budget instead of conservation efforts. The Pennsylvania Environmental Defense Foundation (PEDF) filed the lawsuit in 2014 against an executive order issued by former Republican Gov. Tom Corbett that reversed a moratorium on subsurface leases on state-owned land. During Corbett's term, the General Assembly also decreased appropriations for conservation.

PDEF argued that Corbett and lawmakers violated the state constitution by directing the state Department of Conservation and Natural Resources to lease state land to generate revenue for the state budget. In particular, the group claimed that Corbett and legislators -- as trustees of the state -- had violated Article I, Section 27, a rare environmental rights amendment that reads in part, "The people have a right to clean air, pure water and to the preservation of the natural scenic, historic and esthetic values of the environment." The high court agreed.

"The Commonwealth (including the governor and General Assembly) may not approach our public natural resources as a proprietor, and instead must at all times fulfill its role as trustee," wrote Justice Christine Donohue in the court's opinion. The legislative enactments at issue "do not reflect that the commonwealth complied with its constitutional duties." The case has been remanded to the Commonwealth Court for further proceedings.

Corbett's successor, Democratic Gov. Tom Wolf, signed an executive order in January 2015 reinstating a moratorium on oil and gas leases in state-owned parks and forests. But oil and gas industry opponents have increasingly pointed to the state's environmental rights amendment in their fight against development. Donohue noted in the opinion that residents ratified the amendment "by a margin of nearly four to one" in 1971.

It was given new life in 2013, however, in another landmark case that took some power from the state and undercut the centralized zoning regulations in Act 13 of 2012, which overhauled the state's oil and gas law. In that case, the state’s high court struck down parts of the law and gave municipalities some leeway over shale drilling with more power to change or enforce local zoning ordinances. A plurality of the court found that the centralized zoning regulations in Act 13 violated the environmental rights amendment.

"This decision affirms the self-executing nature of the environmental rights amendment of the Pennsylvania constitution and affirms that the people's rights to clean water and air, and the preservation of a healthy environment, are on par with our other fundamental rights and freedoms, as concluded by the Supreme Court in 2013," said Maya van Rossum of the Delaware Riverkeeper Network, one of the petitioners in the 2013 case.

Three of the justices that heard oral arguments for Tuesday's decision were not on the court at the time the Act 13 opinion was issued. Shale opponents have also so far been unsuccessful in different cases before lower courts arguing that shale drilling is not compatible with the residential-agricultural zones that blanket the state. They've argued that such development in those areas threatens public safety and violates the environmental rights amendment.