The Securities and Exchange Commission late Wednesday declined to make a ruling on a bid to launch what would be the first exchange-traded fund that exclusively tracks the digital currency bitcoin. The regulator said it was instead seeking additional public feedback on the proposal.

The decision is the latest delay for Tyler and Cameron Winklevoss, whose proposed ETF is designed to trade baskets of shares tied to the digital commodity. The twin brothers have been among the most public advocates for a bitcoin ETF, having first announced plans for one in 2013. The pair also run both WinkDex, a bitcoin price index, and Gemini, a bitcoin custodian and exchange.