Clinton should punish the firms under the Iran Sanctions Act, which authorizes sanctions against non-US companies that invest more than 20 million dollars in Iran's oil and gas sectors, they said in the message.
"If firms are violating US law, there must be consequences," the group, led by Republican Representative Mark Kirk and Democratic Representative Ron Klein, said in the message, which was dated Thursday.
"Given Iran's intransigence and the support these companies provide to the Iranians, we urge you to fully enforce the Iran Sanctions Act and levy appropriate sanctions against companies who have violated US law," they said.
The US State Department recently told members of Congress that it had completed a preliminary investigation of companies that could be in violation of the law and has moved on to examining firms it views as "problematic."
US lawmakers have stepped up calls on President Barack Obama to impose sanctions on Iran, as well as companies that do business with Tehran, in response to the Islamic Republic's refusal to freeze its suspect nuclear drive.
Tehran denies Western charges that its atomic program hides an effort to develop nuclear weapons and has rebuffed UN demands that it halt uranium enrichment, which can be a key step towards building an atomic arsenal.
