The group's letter to Obama came as talks between Iran and world powers, aimed at easing fears over the Islamic republic's suspect nuclear drive, made slower-than-hoped-for progress in Vienna.
"As you continue to engage the Iranian government in negotiations about their nuclear program, we urge you to prepare other measures that can be used if diplomacy cannot resolve this conflict," wrote the lawmakers, led by Republican Representative Mark Kirk and Democratic Representative Ron Klein.
The Iran Sanctions Act of 1996 calls for the president to punish non-US firms that invest more than 20 million dollars in Iran's energy sector, but gives the White House the power to waive the sanctions.
Obama, like former presidents Bill Clinton and George W. Bush, has used that authority, even as US firms are barred from doing business with Tehran.
The legislation requires the president to pick two of a menu of sanctions, including denying US bank loans of more than 10 million dollars in one year, a ban on US government contracts, or restrictions on imports.
The lawmakers underlined a finding by the Congressional Research Service that 20 non-US firms may be in violation of the Iran Sanctions Act.
They include Totalfina Elf of France; Italy's ENI; Bow Valley of Canada; the Netherlands' Royal Dutch Shell; Norsk Hydro of Norway; Russia's Lukoil; GVA Consultants of Sweden; Sheer Energy of Canada; LG of South Korea; Norway's Statoil; and Inpex of Japan.
The list also includes China National Offshore Oil Company and Sinopec, both of China; Daelim of South Korea; SKS Ventures of Malaysia; and Brazil's Petrobras.
The lawmakers' letter came amid a rising tide of support in the US Congress for imposing new sanctions on Iran, amid charges that Tehran seeks a nuclear weapons under cover of a civilian atomic energy program.
