The chairman of the U.S. Senate Committee on Homeland Security and Governmental Affairs wants Gov. David Ige to explain what caused a rapid escalation in spending in Hawaii on Medicaid, which is the health care program for the poor and disabled.

Sen. Ron Johnson, (R-Wis.), wrote to Ige and the governors of seven other states today to demand information on what caused state spending increases since the states expanded their Medicaid programs under the Affordable Care Act, also known as Obamacare. Johnson also wants to know what the states are doing to control costs.

Federal spending for Medicaid in Hawaii is “soaring” under the ACA, and spending per enrollee in Medicaid is also increasing exponentially, according to Johnson’s letter.

Johnson cited data from the U.S. Centers for Medicare & Medicaid Services (CMS) that show the costs for new Medicaid beneficiaries in Hawaii increased from $249.1 million in 2014 to $437.4 million in 2015. The cost per enrollee also increased by 73 percent during the same period, according to Johnson.

A spokeswoman for the state Department of Human Services, which runs the Medicaid program in Hawaii, was unable to confirm that spending data. She said no one in the department was available to discuss the concerns raised by Johnson.

One of the key provisions of the ACA was to expand Medicaid to nearly all low-income people under age 65 who have incomes of less than 138 percent of the federal poverty level, according to the Kaiser Family Health Foundation.

Normally the federal government covers about half the cost of Medicaid in Hawaii, but for Hawaii and other states that expanded Medicaid under the ACA, the federal government has been paying 90 percent to 100 percent of the extra cost of the expansion since 2014.

Johnson said the increased costs of Medicaid under the ACA go far beyond initial projections, and he raised similar concerns about increased Medicaid spending in California, Illinois, New York, Michigan, New Hampshire, Ohio and West Virginia.

According to a statement by Johnson, “Federal Medicaid expenditures totalled $246 billion in fiscal year 2009, increased to $299 billion in fiscal year 2014, and are projected to rise 96 percent to $588 billion by 2025,” Johnson said in his letters. “A primary cause of this increase is the ACA Medicaid expansion.”

Johnson asked Ige to provide new enrollment information for Hawaii under the ACA’s Medicaid expansion for 2016 and 2017 as well as the amounts the state has been spending per new enrollee.

The letter also asks for information on why the costs for new enrollees have been increasing so rapidly, and whether the state has conducted or commissioned audits of those costs or the enrollees’ eligibility.

The letter also seeks “all documents and communications between and among employees or contractors of Hawaii” regarding determination of eligibility for the population that is newly eligible under the ACA, and seeks similar records involving payment rates for insurance companies in Hawaii under the ACA expansion.

Johnson is seeking the information by Oct. 11. Johnson is also seeking an array of information about the Medicaid expansion from CMS, according to a statement from his office.