Citadel Securities Says It Learned of Trading Curbs on Twitter

Citadel Securities said it first learned of Robinhood Markets Inc.’s trading restrictions on certain stocks during January’s meme-stock frenzy from Twitter, rebutting accusations that the two firms colluded.

The market-maker fired off a pair of tweets Thursday defending its actions during the upheaval that caused huge rallies in shares of GameStop Corp. and others.

Citadel Securities and its founder Ken Griffin face renewed scrutiny after individual investors filed a class-action lawsuit last week, alleging the trading curbs were enforced as part of a scheme to protect market-makers from losses.

Robinhood, Citadel Securities and other brokerage platforms and clearing ...