Congressional Democrats are pressing a Republican committee chairman to force a pharmaceutical company to turn over documents tied to price hikes imposed earlier this year. U.S.-traded shares of the company, Montreal-based Valeant Pharmaceuticals, are plunging, and had fallen some 20 per cent in five days, as of Monday morning. Valeant was Canada's largest company for some time this year, as Canadian health care stocks soared. It has now fallen to third place. Democrats on the House Committee on Oversight and Government Reform sent a letter to Chairman Jason Chaffetz, R-Utah, asking him to issue a subpoena and to invite the Canadian company to testify next week. Prescription drug prices have come under increasing scrutiny from patients and politicians, including Democratic presidential candidate Hillary Clinton. The Democrats say in their letter that Valeant purchased the rights to congestive heart failure treatment Nitropress and another heart drug, Isuprel, and immediately hiked prices. A representative of Valeant Pharmaceuticals International Inc. did not immediately return a call seeking comment Monday.