I didn't know FR had a Karl Marx PING list.
It is called Willie Green PING list :)
Seriously, Communists did not like trade unions (even if they were using them at times for tactical reasons). They did not like them because they saw them as a compromise that improves the life of workers and turns them away from revolution. They also have seen in trade unions, labor laws and social safety net, the reactionary intrigue of the Church.
Free Market ideology and Marxism are closely related.