House Democrats seeking answers from pharmaceutical companies accused of jacking up prices on vital medications have run into a stone wall in the form of Republican Oversight Committee chair Jason Chaffetz, who counts the drug industry as one of his biggest backers.

Valeant and Turing Pharmaceuticals have both faced mounting criticism in recent weeks. Turing’s CEO, the “Pharma Bro” Martin Shkreli, abruptly increased the price of a critical toxoplasmosis drug from $13.50 per tablet to $750 overnight. Valeant has also been accused of price-gouging, as well as controlling a secret specialty pharmacy that altered prescriptions so its higher-cost medications would go to patients.

Democrats, led by Elijah Cummings in the House and Bernie Sanders in the Senate, have taken aim at both companies, using them to symbolize rising anxiety over the cost of health treatments. For nearly a year, Cummings has sought internal documents and called for hearings through the Oversight Committee, where he’s the ranking member. Valeant and Turing have thus far resisted the document requests.

The Senate launched a bipartisan investigation of Valeant, Turing and other drugmakers this week. But although the House Oversight Committee agreed unanimously to investigate prescription drug prices at the beginning of the year, Chaffetz has refused every request to compel documents, issue subpoenas or schedule hearings.

On Wednesday, Cummings and his Democratic colleagues demanded that Chaffetz reconsider, claiming that he hadn’t even replied to their earlier requests. “Your silence on this … creates the appearance that you do not take seriously a request from nearly half of the members of this committee,” the Democrats wrote.

Given the Republican majority, without Chaffetz’s support, no investigation will be authorized. On Tuesday, Chaffetz said he planned to hold hearings on drug costs at some point, but his spokesperson told the Washington Examiner that no hearings were scheduled.

Chaffetz has received substantial support from the drug industry over the years. Pharmaceutical companies were the top contributor to his campaign in the 2014 election cycle, and No. 2 so far this cycle, according to the Center for Responsive Politics. Overall, pharmaceutical interests have donated over $198,000 to Chaffetz during his career, more than any other industry. He has consistently voted against access to affordable prescription drugs throughout his career, according to the organization Progressive Punch.

The Republican from Utah has carried water for the industry in legislation as well. This January he introduced a bill to extend market exclusivity for “combination drugs” with ingredients already approved by the Food and Drug Administration. This could enable drugmakers to slightly tweak their formulas and extend their monopoly, preventing generic drugs from competition.

Valeant and Turing have not given directly to Chaffetz. Valeant prefers to use its resources on direct lobbying, and Turing CEO Shkreli famously offered a maximum donation to the presidential campaign of Bernie Sanders, who gave the money to a Washington-area AIDS clinic. But by preventing hearings on Valeant and Turing, Chaffetz does protect the wider industry from Congressional inquiry at a time when pressure to limit price hikes is rising. Acting as a human shield for a major business sector can pay off for an ambitious politician who briefly flirted with a candidacy for House Speaker last month.

The industry has already benefited. When Chaffetz said Tuesday that Valeant would not be the sole subject of any hearings, the price of its stock, which has been battered amid the scandal, jumped three points.

House Democrats see opportunity in Chaffetz’s blockade. This week they formed the Affordable Drug Pricing Task Force, hoping to shame Chaffetz into agreeing to an investigation or at least raise awareness of the refusal.

In the letter to Chaffetz, House Democrats seek a November 17 vote on subpoenas to Valeant and Turing. “Of course, it is your prerogative as Chairman to set the Committee’s agenda,” they wrote, “but even if you have no interest in investigating these abuses on behalf of your own constituents, we ask that you not block us from investigating them on behalf of ours.”