LISBON, Portugal (AP) — Portugal is rationing gas as tanker truck drivers begin an open-ended strike over pay.

The government has set a limit of 25 liters (6.6 gallons) for customers at gas stations until further notice.

Some truckers in other sectors of the economy have also joined the walkout that started Monday.

Anticipating gas and fresh food shortages, the center-left Socialist government, which faces a general election in October, is forcing the truckers to provide a minimum volume of supplies.

Authorities hope to limit disruption by demanding that truckers maintain gas supplies to emergency services and airports, provide 75% of normal gas deliveries for public transport systems and 50% to gas stations.

All perishable goods and at least half of normal food supplies must also be delivered to stores.