(Reuters) - The U.S. securities regulator on Wednesday urged U.S. lawmakers not to adopt a bill that aims to create a new legal framework for digital currencies, saying it would undermine existing legal precedent and put capital markets at "immeasurable risk."

The U.S. House of Representatives is expected later on Wednesday to take up the Republican-sponsored Financial Innovation and Technology for the 21st Century Act, which would in part determine which agencies have jurisdiction over which digital assets. The bill's supporters in Congress say it will provide regulatory clarity, helping promote the industry's growth.

The legislation faces an uncertain fate in the U.S. Senate but comes as the U.S. Securities and Exchange Commission (SEC) signals that it will likely approve applications for spot ether exchange-trade funds in a surprising boost to the industry.

But SEC Chair Gary Gensler said in a statement that the bill "would create new regulatory gaps and undermine decades of precedent regarding the oversight of investment contracts, putting investors and capital markets at immeasurable risk."

The bill is backed by crypto supporters and industry organizations who have long viewed Gensler's SEC as an impediment to the wider adoption of digital assets.

Noting high-profile prosecutions, fraud cases, bankruptcies and failures, Gensler has maintained that cryptocurrencies should be subject to the same laws as other assets.

In Wednesday's statement, he said under the bill investment contracts recorded on a blockchain would no longer be deemed securities, denying investors protection under securities laws.

Among other criticisms, Gensler said the bill would also allow issuers of crypto investment contracts to certify themselves that their own products are digital commodities not subject to SEC oversight, leaving the agency just 60 days to challenge this.

(Reporting by Douglas Gillison; editing by Rod Nickel)