Assuming you pay net income tax eliminating this tax credit will raise the amount you owe by 15% of the cost of your transit pass.  So if you pay $100/month it reduced your taxes owed by $180/year.

There is actually a slight irony though in that this tax credit, which was not a refundable credit, probably was of no help at all to a large number of transit riders who don't pay any net income tax in the first place.  For others it might only save them taxes years into the future (many students, for example, might make use of the transit credit to reduce their taxes to $0 and defer more tuition credits to future years).