As the Republican chief economist for the Senate Banking Committee, Piwowar had a front-row seat to the negotiations that produced the Volcker Rule. He has previously announced his intentions to vote against the regulation as it stands, and reiterated Monday that he plans to vote against it unless there is a new proposal.
Five regulatory agencies, including the SEC, will vote Tuesday on the 800-page rule. Volcker himself has said he wishes the rule was simpler.
Much will hang on how the rule is interpreted, according to banking analysts. A less strict interpretation of the rules should be more favorable to U.S. capital markets banks and the U.S. bond market; a strict interpretation could mean that European banks are able to gain more share in capital markets, according to Bernstein Research.
(Read more: Volcker Rule spotlights CEO responsibility)
The rule was reportedly strengthened in the light of the JP Morgan London Whale trading debaclel, where traders engaged in highly risky proprietary trades.
Asset managers at the ICI Global conference called for more co-operation between international authorities to make regulations simpler. Piwowar stressed the importance of cooperation between the SEC and other international agencies. "Sometimes the pushback is that we (the SEC) are trying to slow down rule making, but we have an obligation to do a cost-benefit analysis," he argued.
"The international dimensions to regulation are going to be some of the most important considerations for us."
—By CNBC's Catherine Boyle. Follow her on Twitter