The price of EpiPens, an injectable treatment for serious allergic reactions, has increased by more than 400 percent in the last nine years, and two U.S. Senators are asking the device manufacturer and federal regulators to explain why.

EpiPens have been manufactured by Mylan since 2007, when the pharmaceutical company acquired the autoinjector product. In September 2015, Bloomberg reported the price began going up after Mylan’s purchase, going from a wholesale price of around $100 for a two-pack when Mylan acquired it to $461 in 2015, while in France, where another company manufactures the device, two EpiPens cost $85. According to the New York Times, the two-pack price hit $608 in the U.S. in May 2016.

Concerned about the sharp increases in price, Senate Judiciary Committee Chairman Chucky Grassley, R-Iowa, wrote a letter asking what analyses Mylan has used to determine the EpiPen price, how much the company spends on marketing the device, and what amount of assistance it offers to patients and schools which need to have the device on hand.

“I have heard from one father in Iowa who recently purchased a refill of his daughter’s EpiPen prescription,” Grassley wrote. “He reported that to fill the prescription, he had to pay over $500 for one EpiPen. From other Iowans I have heard concerns about the cost of EpiPens and the need to replace them once a year when they expire. The high cost has also caused some first responders to consider making their own kits with epinephrine vials and syringes.”

Sen. Amy Klobuchar, D-Minnesota, who is the ranking Democrat on the Judiciary Committee’s antitrust subcommittee, went a step further, asking the Federal Trade Commission (FTC) to look into whether Mylan has violated any antitrust laws.

“Although the antitrust laws do not prohibit price gouging, regardless of how unseemly it may be, they do prohibit the use of unreasonable restraints of trade to facilitate or protect a price increase,” Klobuchar said. “The FTC should investigate whether Mylan Pharmaceuticals engaged in activity, such as using incentives or exclusionary contracts with insurers, distributors, or pharmacies, to deny an alternative product access to the market.”

Mylan didn’t comment directly on the letters, but did release a statement detailing efforts to increase access to EpiPens, saying “nearly 80 percent” of commercially insured patients received the device for free thanks to a savings card and more than 700,000 free EpiPens have been distributed to schools. The company also placed blame on insurance plans.

“With the current changes in the healthcare insurance landscape, an increasing number of people and families have enrolled in high deductible health plans, and deductible amounts continue to rise,” Mylan said in its statement. “This current and ongoing shift has presented new challenges for consumers, and now they are bearing more of the cost. This new change to the industry is not an easy challenge to address, but we recognize the need and are committed to working with customers and payors to find solutions to meet the needs of the patients and families we serve.”  

Mylan already has ties to the Senate because its CEO, Heather Bresch, is the daughter of Sen. Joe Manchin, D-West Virginia.