The Securities and Exchange Commission has rejected a hotly disputed proposal to add a new “speed bump,” or split-second trading delay, to the US stock market.

In an order posted on its website on Friday, the SEC disapproved a plan from Cboe Global Markets to introduce a four-millisecond speed bump to one of its exchanges. The regulator called Cboe’s proposal “discriminatory” and said Cboe hadn’t provided enough evidence to show that it would benefit the markets by curbing ultrafast trading strategies.