(Adds plans to carry on with strike)

By Robin Pomeroy

ROME, Dec 11 (Reuters) - Filling stations across Italy ran dry and factories closed on Tuesday as truckers closed motorways for a second day in a protest over high fuel prices and contracts that threatened to bring the economy to a halt.

Blockading strategic points on highways, the truckers stopped cars and freight deliveries in a strike that business leaders said should be broken up by force if necessary.

Fiat shut down its car factories for lack of spare parts and told 22,000 workers to stay at home. Bewildered drivers in Rome were turned away from gas stations displaying hand-written signs to say there was no fuel due to the strike.

"If it doesn't stop by this evening all gas stations will close," said trade association Confesercenti which represents part of the fuel distribution trade. "Already 80 percent of them are without fuel."

Italy's strikes commission said the protest was illegal and the transport ministry issued an injunction to order the truckers back to work as of midnight (2300 GMT Tuesday). However, the truckers vowed to press on anyway.

"The (truckers') associations won't bow to the threats or coaxing of the government," said Conftransporto, one of the groups representing the truckers.

That could mean the strike -- initially announced as a five-day protest -- could continue until Friday if truckers defy the injunction.