This is a new issue for private, non-union businesses. The courts are still working out whether or not requiring arbitration is legal.
Right now if your employer requires arbitration in an employment contract, you must enter arbitration before you can go into court against the employer.
The problem with this, though, is timing. Many agencies require that complaints be filed within a certain time period, and arbitration may cause the employee to miss these deadlines. If you find yourself in this situation, you should contact a local employment attorney.