The U.S. Securities and Exchange Commission (SEC) reiterated the risks of investing in bitcoin futures-focused funds with a staff note on Thursday that underscores the uphill battle U.S. bitcoin exchange-traded funds (ETFs) face.

In an emailed investor bulletin obtained by CoinDesk, staffers “urge investors considering a fund with exposure to the bitcoin futures market to weigh carefully the potential risks and benefits of the investment,” the note said, warning investors that the cryptocurrency as an investment is “highly speculative.”

This is the second recent warning the SEC has sent out in regards to bitcoin’s risk. Last month, it sent out a note to investors highlighting that it may not be safe yet to support an exchange-traded fund under the Investment Advisers Act of 1940 because of Bitcoin’s volatility.

Most bitcoin ETF applications are filed under a different law, the Securities Act of 1933, due to differences in how these laws treat such applications. The SEC has long warned against filing bitcoin products under the 1940 Act.

This warning comes at a time when large traditional banks and investment funds increasingly announce their interest in cryptocurrencies, both personal and corporate. In March, investment bank Morgan Stanley started offering clients access to bitcoin funds and in May Wells Fargo announced it would introduce a cryptocurrency fund.

Just yesterday, CoinDesk reported that investment banker Ken Moelis started looking into the crypto space as a potential business opportunity.