The Philadelphia County Court of Common Pleas has denied Sunoco Pipeline LP’s request to summarily dismiss a lawsuit filed last year by the Clean Air Council (CAC) and two landowners that challenges the constitutionality of the Mariner East 2 pipeline, clearing the way forward for one of the last remaining legal efforts to stop the project.

Judge Linda Carpenter’s ruling means the case can go to trial, which could begin as early as December. The company is currently constructing the 350-mile ME 2 pipeline, which would deliver ethane, butane and propane from processing facilities in Ohio, Pennsylvania and West Virginia to the Marcus Hook Industrial Complex near Philadelphia for distribution to domestic and international markets. Work started in February after the project received key water-crossing and earth disturbance permits from the state Department of Environmental Protection (DEP).

Sunoco has battled landowners throughout the state over its powers of eminent domain. Like others have, the CAC argues that the company shouldn’t be allowed to condemn land because the pipeline has been designed as an interstate system to primarily serve overseas markets and not as an intrastate system that qualifies for eminent domain status. The Pennsylvania Commonwealth Court, however, has upheld the pipeline’s certificates of public convenience from the state Public Utility Commission (PUC). The state Supreme Court has also declined to hear a challenge to Sunoco’s power of eminent domain.

But the CAC is also seeking “relief from uncertainty and insecurity with respect to rights,” under Article I, Section 27 of the state’s constitution, a rare environmental rights amendment. Carpenter certified the landowners and CAC to proceed with their lawsuit last year, ruling that state courts have jurisdiction in the matter because landowner rights under the state constitution are at issue with the matter of property condemnation.

She said much the same on Thursday when she cleared the CAC’s case for trial, noting that the Commonwealth Court has not addressed constitutional issues and reiterating that the court, and not the PUC, is the “proper adjudicating body.”

In certifying the case last year, Carpenter cited the state Supreme Court’s ruling in 2013 that struck down parts of Pennsylvania’s omnibus oil and gas law and gave municipalities and residents more say in oil and gas development. That ruling hinged largely on a reading of the state’s environmental rights amendment and has been invoked since by fossil fuel opponents in their fight against the industry. If a reading of the amendment is somehow included in a negative decision against Sunoco Pipeline — a subsidiary of Energy Transfer Partners LP — it’s unclear how that would affect pipeline development in the state,sources told NGI’s Shale Daily last year shortly after the case was certified.

Other than the Philadelphia County case, the CAC has joined the Delaware Riverkeeper Network and the Mountain Watershed Association in an appeal of the project’s state permits that is currently pending before the Environmental Hearing Board. The groups argue that the project would cause “irreparable harm” to forests and water quality. Given the Commonwealth Court’s actions in the matter and the state Supreme Court’s decision to decline a challenge to Sunoco, it gives the two remaining cases that deal with other issues more import.

Sunoco spokesman Jeffrey Shields said on Friday that the company has no comment on the pending cases as litigation proceeds. He added that the first phase of ME 2 would be complete by the end of the third quarter and said the second phase is expected to be finished sometime next year. Sunoco also said earlier this year that it would proceed with the construction of a third pipeline that would run parallel to ME 2 and be installed shortly after that project is completed.