Big powers: You've been warned
On the sidelines of the UN General Assembly in New York, the three signatories to the agreement said that, in the event of new breaches of the agreement, they would launch a special dispute mechanism.
In that case, the entire nuclear deal would fail and the UN could re-impose sanctions on Iran.
Iran is reported to have begun to breach its obligations under the agreement after the US abandoned it last year and imposed sanctions on the country.
The UN says Iran uses banned uranium enrichment technology, but Iran keeps denying it.