"We need to collectively work to reduce our consumption in order to regain a margin of maneuver," the companies said in an open letter, citing sharp declines in Russian gas shipments as well as limited European electricity production due to maintenance issues.

"Taking action as soon as this summer will allow us to be better prepared at the start of next winter, notably for preserving our gas reserves," they said.

(Reporting by Benjamin Mallet and Mimosa Spencer; Editing by Sandra Maler)