Financial heavyweights including Morgan Stanley, Citadel Securities and BlackRock are exploring potential changes to the US stock market’s circuit breakers after the rarely used mechanisms repeatedly halted trading last month.

The firms belong to a loose industry task force made up mainly of brokerages, trading firms and exchanges that held several rounds of discussions in recent weeks on circuit breakers, said people familiar with the matter. The group is reviewing how circuit breakers worked during the unprecedented selloff in March triggered by concern over the coronavirus pandemic and is identifying possible fixes to recommend to the Securities and Exchange Commission.