
Quoting
flyingron
In Delaware v. Prouse, the court indeed said that stopping cars without cause solely for the purpose of checking for licenses is invalid.
However, in MICHIGAN DEPARTMENT OF STATE POLICE v. SITZ (and others) they've upheld the violation of the 4th amendment (with some dissention) when there's compelling public reason for the stop such as checking for drunk drivers.
So yes, they can stop cars in a discretion neutral way (i.e., they stop everyone, or every third car, or whatever), to check for signs of intoxication. Of course, in the course of this they can ask for your license (and cite you if you are not).
What hasn't been specifically decided is whether such checkpoints for "security" purposes (such as on the approaches to NY bridges) falls under the acceptable compelling reasons. My guess from reading Sitz is that there's a good chance that it could be.
Do you have a specific issue?