What obligates one to have a test governed by DOT guidelines rather than just a run-of-the-mill pre-employment standard test? Obviously, anyone with a CDL, but who else would require DOT standards? I'm going to be working for a firm (hopefully) that gets government contracts. Does any involvement with the government require DOT standards for testing?
The Omnibus Transportation Employee Testing Act, first enacted in 1991, requires drug and alcohol testing of safety-sensitive employees in aviation, trucking, railroads, mass transit, pipelines and other transportation-related industries.

To make the testing process easier, and to minimize mistakes, most other pre-emp U/A's model the testing protocols from the ones established by DOT.