ExxonMobil Oil Corp. dealt a potentially devastating setback Friday to the refinery conversion project along Rosedale Highway by acting to nullify its 2019 agreement to buy renewable diesel from the unfinished plant already more than a year behind schedule and hundreds of millions of dollars over budget.

Refinery owner Global Clean Energy Holdings Inc. quickly rejected the termination notice, saying Sunday that the oil giant must give it until at least Nov. 30 to complete the conversion job because of a deadline-extending provision for unforeseeable circumstances like the COVID-19 pandemic.