BISMARCK, N.D. (AP) — Iowa regulators want owners of the Dakota Access Pipeline to provide expert analysis to back up the company’s claim that doubling the line’s capacity won’t increase the likelihood of a spill, a requirement their counterparts in North Dakota haven’t imposed.

Texas-based Energy Transfer wants to double the capacity of the pipeline to as much as 1.1 million barrels daily to meet growing demand for oil shipments from North Dakota, and is seeking permission for additional pump stations in the Dakotas, Iowa and Illinois to do it. Commissioners in a South Dakota county last year approved a conditional use permit for a pumping station needed for the expansion. Permits in the other states are pending.

The Iowa Utilities Board last week ordered the company to “provide expert explanation of whether the increased flow will increase the amount of oil that will be released if a spill occurs.”

The nonpartisan panel, whose three members all were appointed by a Republican governor, also wants information on pipeline pressure levels currently and if the expansion occurs. The company also must provide “expert explanation” on the effect any additives to the oil would have on the longevity of the pipeline.

The $3.8 billion pipeline has been moving oil from the Dakotas through Iowa to Illinois for more than two years. It was subject to prolonged protests and hundreds of arrests during its construction in North Dakota in late 2016 and early 2017 because it crosses beneath the Missouri River, just north of the Standing Rock Sioux Reservation. The tribe draws its water from the river and fears pollution. Energy Transfer insists the pipeline and its expansion are safe.

Tribal members are asking the North Dakota Public Service Commission to deny the expansion of the pipeline, saying it would “increase both the likelihood and severity of spill incidents.” The company said in court filings that its $40 million pump station built on a 23-acre site would produce only “minimal adverse effects on the environment and the citizens of North Dakota.”

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The North Dakota PSC in November held a hearing on the proposed expansion that was overseen by an administrative law judge. The 17-hour-long hearing was held in Linton, a town of 1,000 along the pipeline’s path and near where a pump station would be placed to increase the line’s capacity from 600,000 barrels per day to as much as 1.1 million barrels. A barrel is 42 gallons.

The three-member, all-GOP elected North Dakota panel has scheduled a “work session” on Thursday in Bismarck to discuss issues raised at the hearing two months ago. PSC spokeswoman Stacy Eberl said no action on the permit request would be taken at the work session, which could extend to at least one more meeting.

Standing Rock attorney Timothy Purdon applauded the action by Iowa regulators requiring expert analysis to back up Energy Transfer’s claims.

“You can’t properly evaluate the safety of the pipeline without this information — and the tribe has asked for this stuff but it’s not part of the record in North Dakota,” Purdon said.