Shares of pharmaceutical giant Mylan Inc. fell over 5.5% in afternoon trading Wednesday as the company faces increased scrutiny over the pricing of its popular EpiPen allergy medication. Interestingly enough, the sell-off in Mylan stock seems to be caused by a tweet sent out by Democratic presidential nominee Hillary Clinton.

At about 2 p.m. EST, Clinton tweeted the following:

EpiPens can be the difference between life and death. There's no justification for these price hikes. https://t.co/O6RbVR6Qim -H

— Hillary Clinton (@HillaryClinton) August 24, 2016

With her account’s signature “-H” marking to signify the message was coming from Clinton herself, the tweet linked to an expansive Facebook post wherein the former First Lady attacked Mylan and its recent price hikes on the EpiPen.

“Over the last several years, Mylan Pharmaceuticals has increased the price of EpiPens by more than 400%. They're now charging up to $600 for a two-EpiPen set that must be replaced every 12-18 months. This both increases out-of-pocket costs for families and first responders, and contributes to higher premiums for all Americans and their employers,” Clinton wrote.

The current frontrunner in what is becoming an increasingly polarizing presidential race would go on to describe Mylan’s behavior as “outrageous” and introduced her plan to address “exorbitant” drug price hikes. Clinton said her plan would require drug companies to explain significant price hikes and prove that additional costs are linked to better patient benefits and value. With that, she called on Mylan to immediately reduce the price of EpiPens.

Although today’s announcement was the first detailed plan to combat the issue, prescription drug reform has been on Clinton’s platform for quite a while. In fact, this isn’t even the first time one of her tweets caused a sell-off.

Back in September of 2015, Clinton tweeted about price gouging in the specialty drug market, which sent biotech ETFS such as (IBB Quick QuoteIBB - Free Report) and (FBT Quick QuoteFBT - Free Report) tumbling (also read: How Hillary Clinton Crushed Biotech ETFs with One Tweet).

As the presidential race continues to heat up, investors should be on the lookout for other policy initiatives that could have a serious effect on the markets.

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