Strikes over wage demands have disrupted the French oil giant's products refining and delivery for the third day on Thursday, threatening supplies at a time of deepening energy instability.

"TotalEnergies has warned us yesterday that we would not be supplied this week," a Tereos spokesperson said in answer to a Reuters question.

"We found substitution supplies to last until at least the end of the week but there have been some adjustments made in production rates," she added. She did specify how much production had slowed, and said the slowdown did not affect all sites.

Tereos provides farmers with fuel for the trucks that bring sugar beets from the fields to the factory where they are processed into sugar and ethanol.

Cristal Union, France's second-largest sugar maker, was not facing disruption to lorry fuel supplies, the group told Reuters.

This comes just as French sugar producers are trying to speed up production ahead of possible energy restrictions or shortages this winter if Russia cuts off gas supplies.

Sugar production is among the most energy-intensive industries. French factories, which usually run between mid-September to late January or early February, are highly reliant on gas to transform their sugar beets into the sweetener.

(Reporting by Sybille de La Hamaide; Editing by David Gregorio)