This would depend on the exact policy of your insurance company. For example, your office co-pay to see the doctor is $25. This type of co-pay usually covers a basic evauluation exam. (you know, the doctor checking to see what might be wrong with you.) BUT, if the doctor determines a special test or procedure is needed while you are in that office visit, then things like that often become a seperate charge ABOVE the NORMAL cost of an office visit, so those charges would probably fall under your insurance guidelines for deductibles and co-pays.
So, you need to check with your insurance company about their policies. Basically, for the doctor's office to charge you more, they would have to have done some procedure or test that is not included in what is considered a "basic office visit" which is what co-pays usually cover. And the additional charge would be the cost of that test or procedure.
So he can not charge you a higher copay — BUT keep in mind your cost for going will depend on what he charges, how big your deductible is and whether or not you are in network
If they are not in network, yes. And, if you get more than an "office visit with $25 copay", also yes.