NEW YORK (Reuters) - Environmental groups are appealing a decision made last month by Illinois regulators to allow the expansion of the Dakota Access oil pipeline (DAPL), according to documents filed with the state on Friday. The Illinois Commerce Commission last month voted to approve an application to roughly double the capacity of Energy Transfer LP"s ET.N 557,000 barrel-per-day crude oil pipeline after legal pushback by environmental groups delayed the vote by about a year. Save Our Illinois Land and Sierra Club, which have led the fight to block the project, filed an application for a rehearing with the ICC, the first step before appealing to state district court. The groups have argued that expanding DAPL, the largest pipeline running out of North Dakota’s Bakken shale basin, posed safety and environmental risks and that an oil market downturn has diminished any need for the project. Dallas-based Energy Transfer has countered that the downturn would be temporary and has said DAPL, which delivers crude to Patoka, Illinois, has had a clean safety record since entering service in 2017. The project has received approvals from several other U.S. states. Energy Transfer was not immediately available for comment. The company is currently embroiled in a bigger legal battle over DAPL, which is under threat of being shut down by a federal district court. Energy Transfer and DAPL’s minority owners are appealing rulings earlier this year by the U.S. District Court for the District of Columbia ordering an environmental review of a portion of the line and vacating one of its key permits. Meanwhile, the district court is considering an injunction to shut the line while the review is carried out. Its decision is expected in the next two months.