Canada Parental Leave Question

Canadian Law allows an individual to earn 40% of their weekly parental leave benefit.

I work for a federally regulated courier company in Canada...It is one of the largest worldwide shipping companies.... We have hourly employees (like myself) and Owner/Operators who own their own truck and are paid by piece and stop count...Whenever these O/O's want to take any vacation or any other days off they must provide a 'relief driver' which the O/O's pay themselves...the company must approve all relief drivers.

While on parental leave, I had arranged to work for one of these O/O's every Friday for the full 37 weeks I would be off...He gets Fridays off and I get to make the extra 40% on top of my parental benefits. Being that parental benefits are only 55% of my regular wage the extra $$$ is MUCH needed...

The management tells me that they will not allow me to do any relief driving while I am on parental leave because it "looks bad" and sets a "bad precedent" to have me wearing the company uniform and being on company property while on parental leave

Does the company have the right to deny me this work even though they are not paying me?