Banks are owned by stockholders, and are operated for the purpose of earning money to pay to the stockholders. (Please don't think I'm saying there's anything wrong with that!) The depositor/borrower of a bank is a customer, nothing more. The stockholders elect a board of directors to oversee the management, and generally pay the board for that work. A stockholder's voting power depends on how many shares of stock he/she holds.
Credit unions are non-profit cooperatives, and as such are "owned" by the members (i.e. the depositors). The members elect directors to oversee management, and directors are generally not compensated for this service. Members each have one vote.
Banks can raise capital by selling more stock.
Because they can't issue stock or bonds, the only way for credit unions to raise capital is by retaining earnings. Because they are nonprofit cooperatives, they don't pay income taxes, but do pay property tax and employment taxes. (Federal credit unions don't pay sales tax, but in most states, state chartered credit unions do.)
Credit unions are subject to almost all of the same consumer protection regulations as banks. CRA is the only exception, and that's because CUs are limited to a specified field of membership. Credit unions are also much more limited in the types of activities they can engage in. Credit unions don't have trust powers, are severely restricted in the types and amount of business loans they can make, and in the types of investments they can make.
So I would disagree (respectfully

) with GenerousLife. While CUs and banks serve some of the same depositors and borrowers, I don't think it's an "unlevel" playing field. They're really on different fields altogether.