This is story about a protection racket being run by rental-car companies.

The fees are not part of the advertised rate, so you hardly notice them when you sign the papers and drive away. But at the end of your trip, the bill is a whopper.

The only good news is that consumers in one state are taking their anger to court. At issue is the price of the collision damage waiver.

When you rent a car, you are offered several options, one of which is the insurance waiver. If you accept it and get in an accident, you may not have to pay anything for car repair. But if you reject it and the car is damaged, you'll have to pay.

Formerly, the waiver wasn't a big item. It cost maybe $2 or $3 a day. Without it, your liability was about $500.

But today, some rental companies hold you liable for $1,000 to $4,000 worth of damage. Others -- including Avis, Budget, Hertz and National -- will charge you for the total value of the car. So now it's pretty risky to turn the waiver down.

The cost is substantial -- maybe $5 to $11 a day, maybe more. On a two-week trip with a $10 waiver, that's $140 in protection money. The price is up because rental companies "can't get collision insurance, or else the price is prohibitive," said Jane Moss of the American Car Rental Association. But firms that hook you with low advertised rates may be raking in the profits by pricing up their waiver.

Savvy travelers will ask their auto insurance agency whether they are covered under the personal policy for collision damage to a car they rent, and to what extent. Often, you're covered in full -- although a few companies put a cap on the coverage, like $2,000, and most cover driving only in the United States and Canada.

But even having your own policy may not give you peace of mind.

If you damage the car, the rental firm may put the entire cost of repairing it (or even replacing it) on your credit card. That's most likely to happen if your personal insurance company has no local representative, or if you don't have collision coverage. And it happens even if you weren't at fault.

One company's staffers were told by a representative of Tropical Car Rental in Hawaii that if a car were damaged, they would be prevented from leaving the island.

Eventually, your own insurer wil pay. But in the meantime, you credit has been tied up -- and you've been making interest payments.

After a collision, the rental company may not wait for your own insurer to inspect the car before repairs are made. Your insurer may dispute the bill, arguing that there's an overcharge. One would hope that the rental firm and your insurer would work peaceably together, and they often do. But you can't count on it.

Some rental companies may charge you for repairs even when you buy the waiver. The fine print on the back of the policy might say that the waiver doesn't apply if you're in any way at fault, if you're driving while sleepy or drunk, if you're off the paved road, or if someone else is driving. The insurer gets to decide whether you were careless or sleepy.

California's attorney general won a lawsuit against Dollar Rent-A-Car, which won't honor the waiver you bought if it thinks you were negligent. That provision is now dead in California, although the company is appealing the decision.

A spokesman says that Dollar took that provision out of all its contracts, but that some of its outlets in other states may be using older contracts. So read before you sign. (The court found that Dollar misrepresented the terms of its waiver and overcharged for repairs.)

Several state insurance departments are trying to regulate waivers. But so far, the rental companies have escaped scrutiny by arguing that a waiver is not insurance.

But there may be another angle of attack. A California court just gave the go-ahead to a lawsuit against Avis, Hertz, Budget and National, arguing that the cost of their waivers is unconscionable. At $9 a day, on a car rented 10 months a year, a rental company is charging $2,700 for collision insurance -- a price an insurance company would kill for.

Right now, buying a waiver is the cost of avoiding trouble. But read the fine print on the back of the contract to see if you're really covered or if the firm can get off the hook. If you find such a company, never rent from them again.