EpiPen Drew Angerer | Getty Images

Will Mylan have to cut another very big check because of the way it's classified its EpiPen for sales to poor people? A group that represents more than 1,200 "safety-net" hospitals is asking the U.S. Justice Department's fraud section to investigate whether big drugmaker Mylan "improperly" overcharged them for sales of its pricey EpiPen anti-allergy device. The group 340B Health, in a letter to the Justice Department, said that Mylan's alleged misclassifying of EpiPen as a generic drug instead of as a brand-name product "would likely have resulted in overcharges" to so-called 340B hospitals. Those hospitals serve significant amounts of poor people and residents of rural communities.

The new allegations parallel ones made over the past several months that Mylan shortchanged Medicaid's drug rebate program as a result of how it classified the auto-injector, which delivers a shot of epinephrine in cases of potentially fatal allergic reactions. Mylan last month agreed with the Justice Department, without admitting wrongdoing, to pay $465 million to settle claims it paid Medicaid less in rebates than it should have been paying as a result of classifying EpiPen as a generic. Mylan also agreed to pay Medicaid's drug rebate program the higher rebate rate charged brand-name drugs starting next April. The 340B hospitals aren't entitled to rebates. But those safety-net hospitals are legally entitled — because of the types of patients they have — to front-end discounts on the price of EpiPens sold through those hospitals.

340B Health, in its letter to the Justice Department, said Mylan's misclassification of EpiPen "would have had a similar impact on establishing" the maximum price 340B hospitals have to pay for EpiPen as that classification had on the Medicaid Drug Rebate Program Randy Barrett, spokesman for 340B Health, told CNBC on Friday that "I don't have any figure on how much 340B hospitals might have been shorted." "What I can say is we've heard from our members that for each package of EpiPens that they've purchased, it appears they could have been overcharged by upwards to $500/package," Barrett wrote in an email. "One hospital reported to us that this would amount to an overcharge of more than $100,000 in the last year," Barrett wrote. That particular hospital was a large one, he said. Both Mylan and the Justice Department declined to comment on the 340B Health letter.