The outlook for the first U.S. exchange-traded fund that invests in Bitcoin just got darker.

The U.S. Securities and Exchange Commission on Thursday again denied an exchange’s request to list a cryptocurrency ETF run by Tyler and Cameron Winklevoss, steepening the odds that any of a clutch of similar proposals will make the grade. The SEC decided to reject the rule change needed for the Winklevoss fund to start trading after reviewing a March 2017 decision, which came to the same conclusion.

Cryptocurrency fans have boosted Bitcoin roughly 40 per cent this month amid a flurry of speculation that the regulator is just weeks away from allowing the first Bitcoin ETF to list in the U.S. At least four requests from exchanges that want to list Bitcoin ETFs are pending. The virtual currency dipped back below the US$8,000 level after the SEC published its decision.

“There’s no way you could not interpret this as a bad sign,” Eric Balchunas, a senior analyst at Bloomberg Intelligence said.

Still, hope remains for other wannabe fund providers, said Balchunas. Several different structures have been submitted to the SEC so one or more of these could still pass muster, he said.

And SEC Commissioner Hester Peirce, who dissented with the decision, said she’s concerned that the agency’s approach undermines investor protection by precluding greater institutionalization of the market. More institutional participation would ameliorate many of the commission’s concerns, Peirce wrote.

“Despite today’s ruling, we look forward to continuing to work with the SEC and remain deeply committed to bringing a regulated bitcoin ETF to market and building the future of money,” Cameron Winklevoss said in a statement.

--With assistance from Olga Kharif.