Employment drug screening.

Inspired by this thread: http://boards.straightdope.com/sdmb/showthread.php?t=455435, when did drug screening, especially urine testing, become financially viable for routine testing by employers and/or law enforcement?
I don’t think it was until well into the 1980’s, but my search skills aren’t helping me to pin it down.

Not exactly what you ask, but it became mandatory for federal employees in Sept 1986.