"In the past two days, as there were operational problems in refining and with the blockades at depots, we have started, in collaboration with the authorities, to use the reserve stocks," Francis Duseux said, as quoted by Le Matin newspaper.
According to the UFIP head, if the situation with the protesters does not improve, the fuel reserves will only last for three months.
Work at six of the eight French refineries has been slowed down or altogether halted by the activists. A fifth of petrol stations nationwide are reportedly experiencing gas shortages.
Protesters blocked all eight fuel depots over the weekend in an effort to push the cabinet of Prime Minister Manuel Valls to scrap an unpopular labor law extending working hours and simplifying firing procedures. On Tuesday, police removed blockades from the Fos-sur-Mer and Lorient refineries.