(Reuters) – A U.S. judge dismissed a lawsuit accusing Robinhood Markets Inc. and other brokerages of wrongly preventing retail investors from buying fast-rising "meme stocks," triggering a sell-off.

In a decision on Wednesday, Chief Judge Cecilia Altonaga of the federal court in Miami found no proof of an illegal conspiracy to cut off social media-fueled trading of GameStop Corp., AMC Entertainment Holdings Inc., Bed Bath & Beyond Inc. and six other stocks.

Investors in the proposed class action said the brokerages and Citadel Securities LLC colluded to halt a "short squeeze" that was causing billions of dollars of losses for Citadel and hedge funds that were betting on falling stock prices.

The investors said the late January trading curbs left them "no option" but to sell at plummeting prices.

But Judge Altonaga said in her 51-page decision that the investors fell "far short" of providing direct evidence of an antitrust conspiracy, despite emails among senior Robinhood and Citadel executives that lent "some credence" to their claims.

"(A)re a few vague and ambiguous emails between two firms in an otherwise lawful, ongoing business relationship enough to nudge plaintiffs' claims across the line from conceivable to plausible?" Judge Altonaga wrote. "The court thinks not."

Judge Altonaga also dismissed related claims against E*Trade Financial Corp. and four other defendants.

Frank Schirripa, a lawyer for the investors, said on Thursday they were disappointed but expected to amend their complaint in the next few weeks.

Robinhood said in a statement: "This further confirms that the conspiracy theory of collusion has no basis in fact."

Citadel said it was pleased with the decision. E*Trade declined to comment. A separate proposed class action accuses Robinhood of negligence.

The meme stock frenzy has been fueled by investors using online forums such as Reddit and Twitter.

Many traded from home because of the COVID-19 pandemic, through brokerages that had eliminated trading commissions.

Last month, the U.S. Securities and Exchange Commission said in a report that markets essentially worked well during the volatility. The regulator did not suggest policy changes.

The case is In re January 2021 Short Squeeze Trading Litigation, U.S. District Court, Southern District of Florida.