A box of masks is shown in the emergency room at Palomar Medical Center in Escondido, California.

Shares of a company selling short-term health insurance plans took a hit Wednesday after Congress members announced they were looking into the practice.

House Democrats, led by Energy and Commerce Chairman Rep. Frank Pallone, D-N.J., are requesting documents from 12 healthcare companies regarding reports of practices like denying coverage and deceiving consumers.

"We are troubled that consumers who sign up for these plans are being misled about the nature of the coverage they are purchasing," the Congress members said in a press release. "Consumers are being denied coverage even for medical care that is rightfully covered under the terms of their contract, through a process known as post claims underwriting."

The House members said they sent letters to companies they say may have denied coverage entirely, charged more based on age, gender or health state, or refused to cover consumers that had pre-existing conditions. Companies under the Congressional microscope either sell or assist consumers in signing Americans up for short-term limited-duration insurance, or STLDI.

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Shares of one of these companies — Health Insurance Innovations — dropped sharply after the news, first reported by Politico. The Tampa, Florida-based company, which trades on the Nasdaq, offers life, critical illness, dental and other insurance products. Shares closed 17 percent lower Wednesday, but are still up more than 15 percent this year.

UnitedHealth Group and Anthem were also among the 12 letter recipients and closed the day slightly higher.

Health care has been divisive issue for both sides of the aisle — especially since the introduction of the Affordable Care Act in 2010. Some Republicans have since moved to repeal the Obama administration's signature healthcare law, while several Democratic presidential candidates are embracing an even more expansive "Medicare-for-all" insurance plan to cover every American.

Raymond James analyst Gregory Peters, who has an "outperform" rating on Health Insurance Innovations, said any investigation by the House Energy and Commerce Committee Democrats "should not come as a surprise."

"We view the sell-off in the stock as an irrational overreaction with zero fundamental basis," Peters wrote in a note to clients Thursday. "The only policy threat to short term health plans is if a Democrat wins the White House in 2021."