By Kate Sullivan | CNN

(CNN) - Sen. Elizabeth Warren unveiled a plan Friday to ban private prisons and detention facilities, should she be elected president in 2020.

The Massachusetts Democrat wrote in a post on Medium that, as president, she would end all contracts the Federal Bureau of Prisons and US Immigration and Customs Enforcements has with private detention providers.

"We need significant reform in both criminal justice and in immigration, to end mass incarceration and all of the unnecessary, cruel, and punitive forms of immigration detention that have taken root in the Trump Administration," Warren wrote.

The US government has a "a basic responsibility to keep the people in its care safe -- not to use their punishment as an opportunity for profit," she said.

The senator would prohibit contractors from charging incarcerated and detained individuals "for basic services they need, like phone calls, bank transfers, and healthcare."

"Washington works hand-in-hand with private prison companies, who spend millions on lobbyists, campaign contributions, and revolving-door hires -- all to turn our criminal and immigration policies into ones that prioritize making them rich instead of keeping us safe," Warren said.

Shares of private prison operators dropped following Warren's released remarks. Warren's campaign, in response, said it was unfazed by the stocks' slump, with campaign spokeswoman and director of communications Kristen Orthman saying, "They shouldn't have a share price because they shouldn't exist."

The senator in her post also lambasted former White House chief of staff and retired Marine Gen. John Kelly for joining the board of directors for Caliburn International, the parent company of Comprehensive Health Services, which operates shelters for unaccompanied migrant children.

The senator previously characterized Kelly's career shift as "corruption at its absolute worst."

"John Kelly oversaw many of the Trump Admin's most morally repugnant immigration policies," she tweeted in May. "Now he could be making big bucks serving on the Board of a company that's profiting from the same cruel plans he put in place."

In her plan, Warren pledged to create an independent Prison Conditions Monitor within the Department of Justice's Office of the Inspector General that would set quality standards, audit and investigate contractors and terminate contractors who fail to abide by the standards.

Warren, at a CNN town hall in April, called for-profit private prisons an "outrage in America" and said they should be banned.

CNN's MJ Lee and Anneken Tappe contributed to this report.