Some interesting info
A Bushman's Song
I asked a cove for shearin' once along the Marthaguy:
"We shear non-union here," says he. "I call it scab," says I.
I looked along the shearin' floor before I turned to go -
There were eight or ten dashed Chinamen a-shearin' in a row.
It was shift, boys, shift, for there wasn't the slightest doubt
It was time to make a shift with the leprosy about.
So I saddled up my horses, and I whistled to my dog,
And I left his scabby station at the old jig-jog.
Andrew Barton ("Banjo") Paterson
Note regarding Paterson's use of the word "leprosy": Chinese were often referred to as "lepers" due to the widely held belief that they carried leprosy, a disease which can render the skin as scabby. Hence, the term "scabs" arose to describe non-unionists and strike-breakers, as Chinese were often used as non-union workers.
(line breaks added by a Joeclone)