The geopolitical equivalent of threading a needle is made even more difficult by elections in both the United States and Iran. Obama's goal, persuading Iran to curb its nuclear program, seems far from assured.
In recent weeks, U.S. officials have crisscrossed the globe to meet allies such as Japan and South Korea that rely heavily on Iranian oil and are worried that the new law may hurt their economies.
The United States also wants to fend off any dramatic spike in oil prices that could hurt its own economy, the top issue for voters who will decide whether Obama is re-elected in November.
U.S. officials say their talks have been productive so far and stress they are not looking to make enemies of their friends, and so will implement the sanctions with care.
"There is flexibility on the sanctions, countries will make their own financial decisions and the United States will work with them," Daniel Glaser, assistant secretary for terrorist financing at the U.S. Treasury, said in an interview.
"The goal here is not to punish any individual country, the goal is to target Iran," he said.
The new law gives Obama the ability to cut off foreign banks, including central banks, from the U.S. financial system if they conduct petroleum-related transactions with Iran's central bank, the main clearing house for its oil exports.