Clinton's proposal comes as part of her plan to fight what she sees as an excessive focus on quick profits in capital markets.
Citing recent surveys of corporate executives, Clinton highlighted the pressures of short-term targets over long term growth, saying that her plan would help fix that problem.
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"It is clear that the system is out of balance, the deck is stacked in too many ways, and powerful pressures and incentives are pushing it even further out of balance," she said. "Quarterly capitalism as developed over recent decades is neither legally required nor economically sound...and fixing it will be good for everyone."
"Real value comes from long-term growth, not short-term profits," she added. "American business needs to break from from the tyranny of today's earning report."
Clinton said she would look to address "very short-term trading" conducted over "days, hours, or even milliseconds."
The presidential contender also proposed eliminating capital gains taxes for some long-term investments in innovative start ups and struggling communities.
"Of course I understand that these changes to the tax code alone will not shift investors' focus from short term to long term overnight, but I believe this reform is an important first step toward removing some of the incentives that push us toward quarterly capitalism," Clinton said, explaining that she plans to propose more reforms later in her campaign.
Clinton's speech also featured an attack on "hit and run activists" who focus on extracting as much value as quickly as possible from companies "no matter how much it discourages and distracts management from pursuing strategies that would add the most long-term value for the company."
She cited iconic companies like Apple and Dow Chemical that "have felt this pressure." (Activists Carl Icahn and Dan Loeb have been involved in Apple and Dow, respectively.)
"So we need a new generation of committed, long-term investors to provide a counter-weight to the hit-and-run activists," Clinton said.