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.