The conservative-dominated council, which oversees legislation passed by the parliament, said aspects of the bill were against Islamic law and the constitution and sent it back to lawmakers for revision.
The bill, narrowly passed by parliament on October 7, is one of four put forward by the government of President Hassan Rouhani in order to meet demands set by the international Financial Action Task Force (FATF), which monitors countries' efforts to tackle money-laundering and terrorist financing.
Last month, the FATF gave Iran another extension to February to update its laws.
"Neither I nor the president can guarantee that all problems will go away if we join (the UN convention), but I guarantee that not joining will provide the US with more excuses to increase our problems," said Iran's Foreign Minister Mohammad Javad Zarif during the parliament debate last month.
A previous bill on the mechanics of monitoring and preventing terrorist financing was signed into law in August.
But two others -- on money-laundering and organised crime -- have also been delayed by higher authorities, including the Guardian Council, after being approved by parliament.
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