A key US Federal Reserve Board member in charge of bank supervision said Tuesday that the Volcker Rule, which limits some speculative bank investments, was working poorly.

The testimony before a congressional oversight committee comes amid lobbying efforts to amend or scale back the law's provisions, which limit certain speculative investments by banks and are legacies of the global financial crisis.

"There is an excessive burden as a result of the Volcker Rule, a great deal of uncertainty and a great deal of cost," Randal Quarles, the Fed's vice chairman for supervision, said in testimony before the House Financial Services Committee.

"That part is unarguable."

Quarles took office in October following his nomination by President Donald Trump. His remarks echoed statements he made in an address last month.

Republicans and industry representatives have long had the Volcker Rule in their crosshairs, making similar arguments to Quarles.

But only Congress can change the law, he added.

"We can't repeal the Volcker Rule and there are certain limits on our ability to make changes that we might otherwise have thought appropriate," said Quarles.

"But there is a lot we can do to increase the certainty of application."

The rule is named for former Federal Reserve Chairman Paul Volcker who argued following the financial crisis that there were unacceptable levels of high-risk speculation by banks that threatened the stability of the entire financial system.

The rule limits certain speculative investments made with a bank's own funds for short-term trading in securities, derivatives and commodity futures -- behaviors that contributed to the financial crisis.

The House of Representatives on Friday adopted legislation that would make the Fed the sole government body charged with enforcing the rule, stripping that authority from four others, including the Treasury's Office of the Comptroller of the Currency and the Securities and Exchange Commission.