The employees at the not for profit agency I work at joined the local teamsters union a few years ago. This week we were informed that there will be a change in our uniion dues starting on the pay reveived tomorrow. The change is as follows: all persons making less than $11 an hour will have their dues reduced, everyone making ^ $11.01 will be paying
2 1/2 times more 37.50. My question is, can the union charge two different amounts of dues to people working for the same agency, getting the same representation based solely on the amount of pay each person receives?

Yes. Check the bylaws of the Union and/or the union contract.

Yes, often in some industries, where employees can make very large amounts they may have several levels of dues.

Yes they can, and its fair if you think on it if your dues are based on a percntage of your pay and not a preset amount .