Green’s Dictionary of Slang

(US) a union official, the inference is of corruption.

1896		Chicago Eagle 19 Sept. 4/4: The Cook County Democratic convention did not make an abject surrender to the Populists and labor skates.
1904		Chicago Eagle 3 Dec. 1/5: The Labor Skates have rung themselves in on the new charter committee.
1912		proceedings US Congress Senate Select Committee to Investigate the Election of William Lorimer n.p.: I said, ‘You are flying pretty high for a labor skate, stopping at the Palmer House.’.
1925		in Virginia Quarterly Rev. 217: Far more serious is the problem of the labor skate.
c.1935		F.P. Dunne Mr Dooley Remembers 31: Some labor leader – labor skate we used to call him.
1949		Monteleone Criminal Sl. (rev. edn) 140: labor skate An official of a labor union.
1953		J. Thompson Savage Night (1991) 56: He’s got a letter from some of the top labor-skates thanking him.
1982		R.S. & H.M. Lynd Middletown in Transition 33: The organizer was just another labor skate.
1993		Adler & Suarez Union Voices 236: Now in his fifties, Greenwood, self-designated ‘flack, hack, and labor skate,’ looks like a caricature of a 1940s’ journalist.