Yes, this is Williamson. Most online sources say he was assisted by Angelo Torres. No one seems to have a date for it, but to my eyes Williamson is using the style he developed in the 1960s after working with John Prentice.
One source stated there were two versions of this comic, the first credited to the Brotherhood of Railroad Trainmen and the second to the United Transportation Union, the BRT's later name. There was a second Cliff Merritt comic, "The Very Candid Candidate," which is posted on this blog:
http://hairygreeneyeball.blogspot.com/2008/07/al-williamsons-candid-candidate.html
In my opinion that one was less Williamson and more assistant (Torres?).
Link to the book:
Cliff Merritt Sets the Record Straight