"The minister has told us that he has not yet made his decision," CGT union official Marie-Claire Cailletaud said after Macron met a delegation of EDF unions.

Macron, who is set to meet EDF's unions again within 10 days, assured them that a decision would not be taken lightly, she said.

Macron told parliament last month that a final investment decision on the 18 billion pound UK project would be taken by early May.

He said at the time that EDF should not delay the investment decision on building two nuclear reactors in Britain as it could risk losing the contract.

The project was announced in October 2013 but a final investment decision has been delayed as EDF has struggled to find partners and financing.

Chinese utility CGN signed up for a one-third stake last October, leaving EDF to fund the rest.

A spokeswoman for Macron was not available for immediate comment.

(Reporting by Geert De Clercq; editing by Michel Rose and Jason Neely)