Sen. Angus King of Maine joined seven other senators in signing a letter to the U.S. Food and Drug Administration questioning a recent decision by the FDA to permit pediatric patients to use OxyContin to control pain.

Under the FDA rule approved in August, pediatric patients ages 11-16 would only be permitted to use OxyContin if they require around-the-clock care and no other opioids or other painkillers had been effective in alleviating pain, according to the FDA. Doctors were previously allowed to prescribe opiates to pediatric patients, but not OxyContin. Prescription opiates, including OxyContin, have been under the spotlight for abuse, and are considered “gateway drugs” for heroin.

“The country is in the midst of an opioid abuse crisis, with more than 2 million Americans aged 12 or older abusing or dependent on opioids,” the letter said. “Opioid overdoses, once almost always due to heroin use, are now increasingly due to abuse of prescription painkillers like OxyContin. We recognize that, in serious cases, children may need appropriately approved and prescribed narcotics. But an increase in the availability of opioids like OxyContin to children — and the potential for abuse — poses a serious U.S. public-health issue.”

The letter called for a review by an independent advisory committee, which the FDA failed to conduct, the letter said.

Maine has experienced a surge in heroin use, with those seeking treatment increasing from 1,115 in 2010 to 3,463 in 2014, according to the Maine Office of Substance Abuse.

Aside from King, Sens. Edward Markey, D-Mass.; Kelly Ayotte, R-N.H.; Joe Manchin, D-W.Va.; Dianne Feinstein, D-Calif.; Tim Kaine, D-Va.; Jeanne Shaheen, D-N.H.; and Dick Durbin, D-Ill. also signed the letter, which was sent Sept. 18.