Employment Minister Jason Kenney tweeted an anti-union joke before deleting the message early Tuesday morning.
"Just wrapped up a meeting with several staff members, at midnight. Good thing they're not unionized," Kenney tweeted shortly after midnight. The tweet was deleted but screencapped by a number of people.
Kenney replaced the tweet with one scrubbed of the jab at unions later that night.
The tweet was noticed by NDP's employment critic Jinny Sims and progressive political site Press Progress.
The Conservative Party passed a party policy at its latest convention that would oppose the mandatory enrollment of workers in unions and allow them to opt out of union dues.