Fidelity Investments, an online brokerage firm, has cut its commission fees to $4.95 and other firms are also cutting prices.

The new commission fee is for U.S. stock and ETF trades made online through Fidelity. The online brokerage firm’s new, lower commission fee comes roughly one month after Charles Schwab Corp (NYSE:SCHW) lowered its commission fee to $6.95 from $8.95 on Feb. 3.

Charles Schwab Corp is now planning to cut its commission fees even more to compete with Fidelity. Starting on March, 3, SCHW will lower its commission fees for ETF trades to $4.95. There will also be a 65-cent fee per contract.

Now that Fidelity and Schwab have started an online trading fees war, other brokerage firms are starting to follow suit. TD Ameritrade Holding Corp. (NASDAQ:AMTD) has announced that it will also be lowering its commission fee. Starting on March 6, its fee will drop from $9.99 to $6.95, reports Investor’s Business Daily.

Fidelity Investments, Charles Schwab Corp, TD Ameritrade Holding Corp. and E*TRADE Financial Corp (NASDAQ:ETFC) are the four largest online brokerage firms. E*TRADE Financial Corp hasn’t jumped in on the trading fee war yet, but it may do so after all the recent commission price cuts from its rivals. ETFC commission fees are sitting at $9.99.

“Online brokers are feeling the competition from robo advisors,” Arielle O’Shea, an investing and retirement specialist at NerdWallet.com, told USA Today. “There are more places for consumers to invest their money at a lower cost. It’s good for investors.”

SCHW stock was up 5%, AMTD stock was up 3% and ETFC stock was also up 3% as of Wednesday morning.