NEW YORK, Oct. 15 (Reuters) — Illinois regulators late on Wednesday approved an expansion of the Dakota Access oil pipeline, the largest pipeline running out of North Dakota’s Bakken shale basin, rejecting a bid by environmental groups to block the project.

The Dakota Access Pipeline can transport about 570,000 barrels per day (bpd) of crude oil from North Dakota to the Midwest, with connections to the Gulf Coast. It had been a source of controversy prior to its completion in 2017, and there is an ongoing legal challenge over whether the line should remain operational after a federal court earlier this year scrapped a key permit.

The Illinois approval is separate from that case.

In an order on Wednesday, the Illinois Commerce Commission said additional pumping stations and equipment needed for the pipeline's capacity to be nearly doubled to 1.1 million bpd are necessary and would promote the security and convenience of the public.

"We are pleased with the decision by the ICC ... this now allows us to proceed with the optimization of the pipeline and allows our labor union partners to go to work," Energy Transfer spokeswoman Lisa Coleman said in an email.

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Environmental groups including Save Our Illinois Land and the Sierra Club, which opposed the expansion, had told the ICC that the oil price downturn caused by the coronavirus pandemic reduced the need for the expansion.

Sierra Club did not immediately respond to a request for comment.

Last month, Energy Transfer told investors it expects to have expanded capacity available on the line by the third quarter of 2021.

In July, the U.S. district court for the District of Columbia determined that the pipeline violated environmental law and vacated its permit to operate on federal land. The company has appealed the district court's decision.

(Reporting by Devika Krishna Kumar in New York and Shariq Khan in Bengaluru; Editing by Steve Orlofsky and David Gregorio)