Green’s Dictionary of Slang

yellow dog n.

also yellow pup

(US) a general term of contempt for a person or thing; also attrib.

[US]Ellis County Star 22 June in Miller & Snell Why the West was Wild 17: Mr. C. fervently thanked God that there was another Justice of the Peace in the county, who would give a lawyer the same rights accorded a ‘yaller dog’ in Court.
[US]‘Bill Nye’ Bill Nye and Boomerang 166: The presiding officer had lost control, and a surging crowd of yellow dogs had the floor.
[US]Times & Democrat (Orangeburg, SC) 4 Mar. 2/1: Yes yaller dorg [...] what do you want?
[US]F. Dumont Dumont’s Joke Book 15: I saw a black dog change color in a minute. Somebody hit it with a stone and it became a ‘yeller’ dog.
[US]S.E. White Arizona Nights III 306: Don’t leave me here to be crushed in this vice. You wouldn’t do that to a yellow dog.
[UK]Gem 23 Sept. 21: You’re a yellow pup!
[US]J. London Star Rover (1963) 9: He was a sniveling cur of a yellow dog.
[US]Dos Passos Three Soldiers 182: He remembered that Andy was crazy — a ‘yaller dog’, Judkins had called him.
[US]H.C. Witwer Fighting Blood 307: We’re gonna tar and feather the yellah dog!
[US]M. West Pleasure Man (1997) II ii: Why, you yellow pup – you couldn’t even lick a lollypop!
[Aus]‘Banjo’ Paterson Shearer’s Colt 160: When he wants a friend you run out on him like a yeller dog.
[US]Dos Passos Adventures of a Young Man 230: He’s a yellow dawg but he ain’t so crooked as some.
[US](con. 1860s) B.I. Wiley Life of Johnny Reb 343: The feeling that such officers used family influence to get soft positions caused then to be designated by some as yellow sheep-killing dogs, which term was soon shortened to ‘yaller dogs.’.
[US]W.D. Overholser Buckaroo’s Code (1948) 120: ‘You’re a yellow dog,’ Cotton shouted.
[US]B. Hecht Sensualists (1961) 106: Husbands are all yellow dogs.
[US]R. Coover Public Burning (1979) 105: Willis Robertson, yellow-dog Democrat from Virginia.
[US]W.T. Vollmann You Bright and Risen Angels (1988) 60: You prick-nosed stingy yellowdog.
[US]H. Rawson Dict. of Invective (1991) 123: yellow dog. Originally, a mongrel or cur, and popularized by Abraham Lincoln as a general symbol of inferiority.

In compounds

yellow dog contract (n.)

(US) an employee’s work contract forbidding union membership.

Coal Age 4 66/2: Miners who were evicted from their homes on that company's property, under the term of what the miners call ‘the yellow dog contract’.
Motorman and Conductor Oct. 34/1: Yellow dog contracts [...] provide that the miner shall not join a union while in the employ of the company [DA].
[UK]W. White A Man Called White 106: The American Federation of Labor had also protested Parkers confirmation because of decisions he had rendered in upholding so-called ‘yellow-dog’ contracts.
[US] (ref. to 1956) Maledicta III:2 157: yellow-dog contract n [DAS 1956] One between a worker and an employer in which the worker agrees not to remain in or join a union.
[US]H. Rawson Dict. of Invective (1991) 123: Yellow-dog contracts, since declared illegal, required workers to agree before being hired not to join a union during their term of employment.