North Dakota regulators on Wednesday approved expanding the Dakota Access pipeline, despite concerns from environmentalists and Native Americans who said the plan makes an oil spill more likely.

The 3-0 vote by the Public Service Commission clears one hurdle to double the pipeline's capacity to 1.1 million barrels of crude oil per day, but the proposal needs additional permits and may face legal challenges.

The pipeline crosses beneath the Missouri River, just north of the Standing Rock Sioux Reservation, moving North Dakota oil through South Dakota and Iowa to a shipping point in Illinois. Tribe members, environmentalists and their supporters argued that the pipeline damages sacred sites and could pollute the water source, but the federal government approved the project three years ago.

Energy Transfer, the developer of the pipeline that triggered protests three years ago, said the expansion will meet growing demands for oil shipments from North Dakota, the nation's No.2 oil producer after Texas. The proposal doesn't require additional pipelines or rail shipments, the company said, and involves building a $40 million pump station near Linton in south-central North Dakota.

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The proposal includes plans for leak detection and worst-case spill responses, said Commissioner Julie Fedorchak, that the board believes meet or exceed the state's permitting requirements.

The Standing Rock Sioux Tribe objected the vote in a statement, adding it shows "little or no consideration" of how the expansion may affect family farms and public health.

"We will continue to examine what additional legal recourse we have to protect our people, our water, and our lands from this dangerous decision," said the tribe, which has continued to protest the pipeline since its construction in late 2016 and early 2017.

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Energy Transfer has said expanding the pipeline is safe and does not increase the risk for an oil spill. In its court filings, the company said the proposed pump station would produce only “minimal adverse effects on the environment and the citizens of North Dakota.”

The company next needs regulators in Iowa and Illinois to approve the expansion permit. Construction should take about 10 months once approved, Energy Transfer said.

Contributing: The Associated Press