A surge of buying in stocks including AMC Entertainment and GameStoptriggered by activist retail investors on Reddit and other social platforms — this week overwhelmed no-fee investment app Robinhood’s ability to cover the frenzied trading.

After Robinhood on Thursday suspended buying of shares in AMC, GameStop, BlackBerry and 10 other volatile stocks, the company raised an emergency $1 billion in funding from investors including VC firms Sequoia Capital and Ribbit Capital, the New York Times reported.

“Starting tomorrow, we plan to allow limited buys of these securities,” Robinhood said in a blog post Thursday. “We’ll continue to monitor the situation and may make adjustments as needed. To be clear, this was a risk-management decision, and was not made on the direction of the market makers we route to.”

The campaign to drive up the stock prices of certain companies, led by users on Reddit’s r/wallstreetbets forum, has been motivated by a desire to punish hedge funds that have shorted stocks (i.e., placed bets that stock prices will decline).

The grassroots movement has led to massive swings in the prices of the targeted companies: Shares of AMC — which had faced the prospect of bankruptcy because its theaters have largely lain fallow during COVID before raising more than $900 million in its own emergency financing — boomed more than 300% Wednesday then fell 57% yesterday. In premarket trading Friday, AMC stock is up more than 50%.

Robinhood said its halt of stock buys of AMC and the other high-volume stocks — while it allowed users to sell their holdings — was due to regulatory requirements. “As a brokerage firm, we have many financial requirements,” Robinhood said in a blog post Thursday. “Some of these requirements fluctuate based on volatility in the markets and can be substantial in the current environment.”

Robinhood’s suspension of the trades elicited calls from politicos including Rep. Alexandria Ocasio-Cortez (D-N.Y.) and GOP Sen. Ted Cruz for an investigation as well as several lawsuits from frustrated users.

The fundamental problem at play is the lack of regulatory oversight over attempts to manipulate markets by bad actors online, Joshua Mitts, a professor at Columbia Law School who specializes in regulation of capital markets, told Variety Thursday. It’s “basically a free-for-all at the intersection of social media and financial markets,” Mitts said. “The SEC has largely been inactive when it comes to regulating trading in connection with social-media campaigns.”

Founded in 2013, Robinhood says its mission is “to democratize finance for all.” Ordinarily, the company routes buy and sell orders for stocks to market makers (third-party securities clearinghouses) that “typically offer better prices than public exchanges.” Robinhood has deals with those market makers, which provide rebates to the brokerage on trades.

On Friday, the SEC’s four current commissioners issued a statement saying the agency “is closely monitoring and evaluating the extreme price volatility of certain stocks’ trading prices over the past several days.” They said the commission “will closely review actions taken by regulated entities that may disadvantage investors or otherwise unduly inhibit their ability to trade certain securities” and said the SEC “will act to protect retail investors when the facts demonstrate abusive or manipulative trading activity that is prohibited by the federal securities laws.”