(NBC) – A California woman is suing CVS, the largest pharmacy chain in America, for allegedly charging more to customers who use insurance to pay for certain generic prescriptions.

The lawsuit, filed on Monday, accuses CVS Health Corporation of participating in a “fraudulent scheme” and claims the plaintiff, Megan Schultz, paid $165.68 for a prescription in July that, had she bought without using insurance, would have only cost $92.

“CVS never told her that paying in cash would allow her to pay 45% less for the drug; instead, CVS remained silent and took her money — knowing full well that no reasonable consumer would make such a choice,” the complaint says.

The problem, it alleges, is with co-pays sent back to pharmacy benefit managers, or PBMs — the intermediary between insurance companies and pharmacies who negotiate the prices that insurance companies have to pay the pharmacies. PBMs control which pharmacies are in-network for the insurers, incentivizing CVS to offer them a portion of their sales so they can get more clients.

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