The company I work for forced us to either participate in a "team building" exercise or take a vacation day. Can they legally dictate to you to take a vacation day????????????? I would have rather worked then participated in the team builder. I had no choice and participated in the team builder, which was 45 miles away from where I work. They are now telling us they will only pay mileage one way. I guess because we went home after the team builder was done. Is this legal? Because I just feel like I am forced into this situation. I had no vacation time to use because I just got back from vacation. So I had no other choice.:confused:

Yes, they may. The employer can dictate when vacation may or must be taken. Personally, I hate 99% of those "team-building exercises" too. But the choice given was attend or take the day off as vacation.
See #6 here:
http://www.dir.ca.gov/dlse/FAQ_Vacation.htm

How far is your normal commute, round-trip? Did you go to the site directly from home? Theoretically, they should be reimbursing you for the incremental mileage.