That's not the way unions themselves use the word.
https://www.espn.com/mlb/story/_/id/24904995/boston-union-ca...
"Boston union calls Yankees 'scabs' for crossing hotel picket line"
Or, imagine a nurses' strike, but I as a patient don't honor their strike, am I a scab?
The parent comment was absolutely correct in saying that you are trying to co-opt the actual definition to serve your goals, as the word has nothing to do with being a customer.
[1] https://www.nytimes.com/2019/04/22/us/stop-shop-strike.html
Your comment seems to not really make much sense since UAW and other unions are currently involved in calling for boycotts of Mexico-assembled GM vehicles.