Kim, presumably an officer needs probable cause to request a breathalizer test, and in fact even to stop an individual car. So far, however, courts have ruled that the public good achieved by "drunk driver checkpoints" supersedes the concern for the accessory violation of the right to freedom from unnecessary search and seizure. Once the car is stopped and the police can observe the driver's behavior and any other clues (odor of alcohol, empty booze containers inside, etc.), they can usually claim some sort of probable cause to administer the breath test.

In a similar vein, law officers go on "fishing expeditions" whenever they scan a highway with speed radar guns. They can probably squirm around any protest by claiming it looked like that car was speeding and they therefore had probable cause.

It's the old trade-off between freedom and security. Was it Benjamin Franklin who said, "He who gives up freedom for security deserves neither" (or something like that)?