Unless the union is able to explicitly explain their claim the Uber is somehow unfair to drivers, to me sounds like the union is just complaining they not getting their member dues.
Possible I missed something, so here are my sources:
How much Uber drivers make in Switzerland
https://www.swissinfo.ch/eng/ride-sharing-app-_uber-reaches-...
Taxi Driver Average Salary in Switzerland
http://www.salaryexplorer.com/salary-survey.php?loc=210&loct...