Its against the law for them to ask you to strip. You are not a criminal under arrest. You are taking a test for a job.
You won't be asked to give 2 samples unless you had been suspected of adulteration or submitting a sample outside of the proper temperature range (in such a case, the 2nd sample is submitted under direct observation).

In split-sample cases, one sample is submitted (45ml), then the tech splits it to 30ml for sample A, 15ml for sample B.