Fidelity Investments has joined its major competitors in offering zero-commission online trades as the brokerage industry continues its low-fee makeover.

The company tweeted that it has eliminated commissions on all its trades involving stocks, options and exchange-traded funds, a burgeoning $4 trillion industry that has remade the way Fidelity and its peers do business.

In the latest chapter of an ongoing fee war, Charles Schwab, E-Trade, TD Ameritrade and Interactive Brokers all announced recently that they were dropping trading commissions. The news sent shares of the companies reeling as the revenue drivers for the companies became even cloudier.

Fidelity boasts $2.46 trillion in assets that it manages for clients and has 21.8 million accounts with total assets of $6.8 trillion. The firm previously charged $4.95 for trades.

"With this decision, Fidelity is taking a different path from the industry," Kathleen Murphy, president of Fidelity Investments' personal investing business. said in a statement. "We are providing customers unmatched value while challenging industry practices that appear to give value in one place when they are actually having customers pay in other ways."

While its competitors, particularly Schwab, made high-profile announcements when they eliminated trading commissions, Fidelity chose to go lower-key.

In its statement, the firm said it also would automatically direct client money into higher-yielding money market accounts and is offering zero payment for order flow on where it sends its trades for execution.

"We made this decision after careful consideration to our clients and ensuring we are satisfying their full needs," Murphy added.