The U.S. Securities and Exchange Commission (SEC) is once again seeking comments on a potential bitcoin-based exchange-traded fund (ETF).

The securities regulator called for comments on a proposal by the Cboe to list and trade the SolidX Bitcoin Shares, an ETF that was in turn proposed by the VanEck SolidX Bitcoin Trust, according to documents published Tuesday.

The trust will invest in bitcoin only, the document notes - as its net assets will "consist of bitcoin held by the Trust utilizing a secure process."

The Cboe's filings indicate that the Trust will invest solely in bitcoin and shares in the vehicle will subsequently reflect the world's largest cryptocurrency's price. While its operators will buy or sell bitcoin as needed, "the Trust is not actively managed," according to the document.

SEC is asking for comments on this proposed rule change from "interested persons."

As previously reported by CoinDesk, this particular ETF is the result of investment firm VanEck partnering with blockchain startup SolidX. It is VanEck's third attempt to create a bitcoin investment vehicle.

VanEck CEO Jan van Eck said he believes bitcoin is "a legitimate investment option, as a type of 'digital gold' that may make sense for investors' portfolios," despite regulatory hurdles they've met previously.

"We believe that collectively we will build something that may be better than other constructs currently making their way through the regulatory process. A properly constructed physically-backed bitcoin ETF will be designed to provide exposure to the price of bitcoin, and an insurance component will help protect shareholders against the operational risks of sourcing and holding bitcoin," he told CoinDesk at the time.

While various companies have attempted to list bitcoin ETFs in the past, the SEC has forced withdrawals in every case. The regulator has previously stated that it is concerned with the cryptocurrency's volatility and liquidity, among other issues.

Bitcoin image via Shutterstock