• Investors have been keeping an eye on the SEC and whether the regulator will approve the ether ETF by late May.
• Issuers of the first U.S. spot bitcoin ETF, including VanEck and CoinShares, are not confident that the SEC will approve ether applications.
• VanEck CEO Jan van Eck said he thinks the SEC will most likely reject the firm's ether ETF application.

PARIS — Issuers of spot bitcoin exchange-traded funds on Tuesday say the U.S. Securities and Exchange Commission is unlikely to approve such a product for the cryptocurrency ether.

The regulator has a late May deadline to conclude its review on an ether ETF. That comes after the SEC in March delayed its original deadline for a decision on the ether ETF application.

Companies ranging from BlackRock to Fidelity and VanEck, which issued spot bitcoin ETFs this year, have been waiting for approval of an ether product.

Some issuers are not confident the SEC will greenlight the ether applications.

"We were the first to file as well for ethereum in the U.S., and we and [Ark Invest CEO] Cathy Wood, are kind of the first in line for May, I guess, to probably be rejected," VanEck CEO Jan van Eck told CNBC's Arjun Kharpal at the Paris Blockchain Week crypto event in France.

Ark Invest was not immediately available for comment when contacted by CNBC.

"The way the legal process goes is the regulators will give you comments on your application, and that happened for weeks and weeks before the bitcoin ETFs — and right now, pins are dropping as far as ethereum is concerned," van Eck added.

Enthusiasm has been mounting among the crypto community for an ether ETF, ever since the SEC approved the first spot bitcoin ETFs in January.

The ether price has been climbing this past week on the back of hopes that the SEC will approve an ether-backed ETF.

The token is up about 10% in the last seven days, according to CoinGecko data.

However, the U.S. regulator has signaled that it might not be so willing to approve such an investment product.

SEC Chair Gary Gensler has previously stressed that "the vast majority of crypto assets are investment contracts and thus subject to the federal securities laws," in the agency's view.

This complicates matters for an ether ETF.

"We are observing the ethereum decision very, very closely," CoinShares CEO Jean-Marie Mognetti told CNBC on Tuesday. "CoinShares was not in the race for the bitcoin ETF until three months before the approval, and we managed to qualify ourselves at the last minute."

He was equally pessimistic over the odds of gaining such an approval in the short term.

CoinShares is not one of the companies in the running for an ether ETF in the U.S.

"I don't see anything being approved this side of the year," he noted, suggesting it may be difficult to gain SEC approval for proof of stake — a protocol specific to blockchain.

Bitcoin is underpinned by a different protocol, known as proof of work, where volunteer miners validate transactions and mint new tokens.

The SEC has not taken issue with proof of work from a securities law standpoint.