Martin Shkreli, CEO of Turing Pharmaceuticals, just got a letter from the US Senate. And it’s not a nice letter (PDF).

It was sent by US Senators Susan Collins (R-Maine) and Claire McCaskill (D-Mo.), leaders of the Senate Special Committee on Aging, who are concerned by recent drug pricing practices. In addition to Shkreli, the senators sent letters to the heads of three other pharmaceutical companies, namely Valeant Pharmaceuticals, Retrophin, Inc., and Rodelis Therapeutics.

Recent actions within the pharmaceutical industry “have looked like little more than price gouging,” Sen. McCaskill noted in a press release. The release made particular note of Turing’s recent move to increase the price of the drug Daraprim from $13.50 a pill to $750.

Such price hikes on old drugs stand to raise the overall cost of healthcare for Americans, particularly vulnerable senior citizens, by hundreds of millions of dollars each year, the senators wrote. The goal of the committee is to understand the causes and impacts of, as well as potential solutions to the price increases. The committee also plans to investigate the companies' mergers and acquisitions, as well as the Food and Drug Administration’s role in the approval and distribution protocol for generic drugs.

In their letters to the pharmaceutical companies, the senators requested a slew of documents, including internal communications, pricing plans, communication with the FDA, and financial documents.

The committee has tentatively scheduled an initial hearing for December 9, 2015.