The day came for Irans 4th step back out of its JCPOA commitments. Iran took its 4th step in reducing its JCPOA commitments, as it had announced earlier, because after the US left the deal the EU failed actually to compensate for the loss Iran suffered.
The JCPOA or Iran Nuclear Deal of 2015 allows Iran a 3.67 percent limit for uranium enrichment. But Iran will now be enriching uranium to 5 percent. The Deal was signed between Iran and the P5+1. That was to limit Irans nuclear programme, in return for lifting nuclear-related economic UN sanctions off the country.
On 8th May 2018 the US unilaterally pulled out of the multilateral international nuclear deal, and re-imposed and re-enforced sanctions on Iran; no longer as UN sanctions but as US maximum-pressure sanctions.
Iran took the 4th step in reducing its commitments including the injection of uranium hexafluoride gas (UF6) into Fordows centrifuges, pouring concrete for a new reactor at the Bushehr power plant and operating 60 IR-6 advanced centrifuges.