Origin of the "Pink Slip"

[Michael Stroh]

I'm trying to pin down the origin of the term "pink slip" for a story I'm
working on.  But so far none of the leading labor scholars I've consulted
seem to have a clue, which seems odd considering how often the term is used
(especially these days).

Anybody have any thoughts on the expression's historical roots?

Best,
Mike Stroh
reporter
The Baltimore Sun
Baltimore, MD