If you wish to protest the increase you can hold a "party" in which whatever goods are named in the dialogue will be thrown away. It tends to be whatever goods you have the most of on hand at the time. This initiates a boycott of those goods. Your tax rate will not increase this time, and you cannot buy or sell them in Europe without paying a large penalty in gold. The historical significance of this should be obvious, but from a game economy standpoint, it is probably a greater hindrance than benefit.
Jakob Fugger can be very helpful in eliminating boycotts.