BEIRUT -- Police forces were deployed on main roads across Lebanon to enforce a anti-pollution law taking effect Saturday that bans taxi drivers from running their vehicles on heating oil.

Patrols circulated on main roads in Beirut, other major cities and main highways across the country, which witnessed relatively light traffic, AFP correspondents said.

Many taxi drivers apparently stayed home, either because they had not modified their engines to run on gasoline or in response to union calls to stay off the roads and protest on Monday.

Checkpoints were erected, and motorcycle police drove between cars in traffic jams to check whether cabs were emitting black smoke from their exhausts.

At least two taxis were seized at a Beirut intersection to be towed away, their drivers having their licenses confiscated and being issued with tickets.

A police officer told AFP violators risked large fines and prison terms of about two months.

A number of mechanics, mostly in the capital's densely populated suburbs and in other large cities, were seen converting taxi diesel engines to run on gasoline.

If Saturday's law enforcement efforts target the country's 30,000 taxis, tens of thousands of minibuses will continue to run heating oil, as a deadline for them to switch over is not until July 15.

Trucks and buses are exempted from the ban.

Confrontations between the government and the angry taxi drivers seemed to have been averted after drivers union Chief Abdel-Amir Najdeh backed down on calls for protests over the weekend.

Najdeh was quoted by Beirut newspapers as asking drivers to "stay home" and hinting that protests could be held on Monday.

The state has promised a carrot to keep the protests down. It will pay out between 666 and 1,333 dollars per driver -- a total cost to the taxpayer in a country sinking under a huge debt burden of about 29 million dollars.

Since 1995, the government has turned a blind eye on diesel engines in a bid to reduce transportation costs, but failed to import diesel fuel. As a result, drivers used the more highly polluting heating oil, which brought them larger returns because it was much cheaper than gasoline.

After witnessing the government determination to enforce the law, taxi drivers focused their demand on subsidies for gasoline prices.