The U.S. Army will grant the final permit for the controversial Dakota Access oil pipeline after an order from President Donald Trump to expedite the project despite opposition from Native American tribes and climate activists.

In a court filing on Tuesday, the Army said that it would allow the final section of the line to tunnel under North Dakota’s Lake Oahe, part of the Missouri River system. This could enable the $3.8 billion pipeline to begin operation as soon as June.

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Deborah Sivas, professor of environmental law at Stanford and director of Stanford’s Environmental Law Clinic, said a challenge by the tribe would likely rely on the reasons the Army Corps itself gave for why more review was needed in December.

“The tribe will probably argue that an abrupt reversal without a sufficient explanation for why the additional analysis is not necessary is arbitrary and should, therefore, be set aside,” she said in an email.