Clinton said at an Iowa campaign stop on Tuesday that she would lay out her plan to rein in Wall Street "abuses" within the next week.

"The growth of high-frequency trading has unnecessarily burdened our markets and enabled unfair and abusive trading strategies," the aide said.

The tax would target securities transactions with excessive levels of order cancellations, which destabilize the markets, a campaign aide said.

U.S. Democratic presidential candidate Hillary Clinton will propose a tax on high-frequency trading, her campaign said late Wednesday.

Clinton said her plan would focus on more than banks, taking into account any kind of financial institution that causes disruption in the marketplace.

The tax on high-frequency trading will be part of that plan, which would also include changing stock market rules to increase transparency and minimize conflicts of interest, according to her campaign.

Clinton will call on the Securities and Exchange Commission to pursue changes that ensure equity markets favor investors over high-frequency traders and those that use so-called "dark pools," which are private networks that allow institutions to trade with one another outside traditional stock exchanges.

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Clinton's Wall Street proposals are being closely watched by progressives within the Democratic Party who have called on her to take an aggressive stance towards the financial industry.

Clinton's campaign confirmed that the proposal for tax on high-frequency trading was crafted with input from her campaign chief financial officer Gary Gensler. Gensler's hiring was seen as a move to both contain the high costs that plagued Clinton's 2008 presidential bid and send a signal that she would take a hard line on Wall Street.

Gensler, as former chairman of the Commodities Futures Trading Commission from 2009 to 2014, during the rise of high-frequency trading, was seen as a tough regulator.