Pedestrians pass in front of a TD Ameritrade location in San Francisco, California.

Interactive Brokers will now make any amount of your stock trades without commission fees, threatening rival brokerage firms.

Shares of retail brokerage firms TD Ameritrade, Charles Schwab, and E-Trade Financial all traded down Thursday afternoon upon the announcement.

Shares of TD Ameritrade sank 6.5%, Charles Schwab dipped 2.2% and E-Trade Financial fell 4.8%.

Interactive Brokers said its new product, called IBKR Lite, will "provide commission-free, unlimited trades on US exchange-listed stocks and Exchange Traded Funds," the company said in a release.

IBKR Lite will have zero commissions on U.S. stocks and ETFs, no account minimums, no inactivity fees, free market data, in addition to other features, the company said.

The new product will be available in October.

"In order to attract a broader audience, we wanted to remove any impediments to opening an IBKR account," Thomas Peterffy, chairman and CEO of Interactive Brokers, said in a release.

Correction: Shares of retail brokerage firms TD Ameritrade, Charles Schwab, and E-Trade Financial all traded down Thursday afternoon.