Democratic presidential candidate Sen. Bernie Sanders fired back Monday at Martin Shkreli, the Turning Pharmaceuticals CEO who became the "most hated man on the Internet" after raising the price of a lifesaving drug from $13.50 to $750 per pill. In an email to supporters, Sanders explained why he was rejecting a $2,700 donation from the former hedge fund manager.

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"The economic and political systems of this country are stacked against ordinary Americans," Sanders wrote. "The rich get richer and use their wealth to buy elections and legislation. Saying to Wall Street and the drug companies and the rest of the billionaire class, 'please, do the right thing' while taking their money to fund your campaign is both naive and ultimately ineffective."

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In an effort to secure a private meeting to discuss the pharmaceutical industry with Sanders, Shkreli made the maximum individual contribution to his campaign in September. But Sanders, who has led a largely grassroots campaign, said he would not accept Shkreli's money and would instead donate it to an AIDS clinic in Washington D.C.

"We are not keeping the money from this poster boy for drug company greed," campaign spokesman Michael Briggs told the Boston Globe.

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Last month, Sanders launched an investigation into the price hike of Daraprim, a drug used to treat cancer and AIDS patients, writing in a statement that Shkreli "is holding hostage the patients who rely on this lifesaving medication, as well as the hospitals that administer it, by charging unconscionable prices for a drug on which he has a monopoly—just because he can."

Though Shkreli said that he would lower the price of Daraprim nearly a month ago, he has yet to do so. And in the weeks since Sanders first called out the pharmaceutical executive, Shkreli has gone on the offensive, posting memes and messages on Twitter that attack Sanders' policy proposals. On Sunday, he went so far as to fake a broken wrist, trolling followers who were tricked into thinking that he had punched a wall out of anger directed at the presidential candidate.

But Sanders isn't getting involved in Shkreli's social media spat. Instead, he wants to make an example of the Turing CEO by highlighting the need for campaign finance reform.

"So far we've funded our campaign with more than 1.3 million contributions of about $30 a piece," Sanders wrote. "Small contributions of whatever regular folks can afford will win the fight against corporate greed and beat the influence of oligarchs like Martin Shkreli."

A few hours after the email from Sanders' campaign went out, Shkreli posted a photo on Twitter that appeared to show two different versions of the email.

He followed up minutes later, saying that Sanders "raised the donation requested from his supporters by 755 percent in one day."