French President Nicolas Sarkozy has won a strategic battle as protests over pension reforms show no sign of ending.
Riot police have forced open a fuel refinery at Grandpuits, east of Paris. It is the closest source of gasoline supplies to the capital.
However scuffles broke out between officers and workers who had linked arms and refused to move.
The operation came as the French Senate is about to vote on a bill at the heart of the union's anger, after the government short-circuited a protracted debate.
The idea of raising the retirement age from 60 to 62 has prompted numerous street protests, with tension spilling over into violence and vandalism after months of strikes and demonstrations.
The Senate is near-certain to approve the measure before the weekend.
Sarkozy ordered regional authorities to intervene and force open depots, accusing the strikers of holding ordinary people and the French economy "hostage."
He said overhauling the pension system is vital to ensuring that future generations receive any pensions at all.
It is a choice many European governments are facing as populations live longer and government debts soar.
However, French unions say retirement at 60 is a hard-earned right, and that the working class is unfairly punished by the pension reform.
They fear this reform will herald the end of an entire network of welfare benefits that make France an enviable place to work and live.