When can an employer change your role/job description/duties/ without your consent?

I work for a large corporation as a senior business analyst. Management informed my team that we were to cease our normal job functions and man the help desk fielding support calls for the better part of a year. My team consists of professionals (business analysts, developers, QA) and the support desk is basically unskilled labor with no overlap in duties with what any of us was hired to do. We all signed contracts when we were hired and within those contracts were our roles and responsibilities as you would expect. None of the contracts mentions anything about support desk responsibilities or that we would be subject to changing responsibilities without consent. In a nutshell, none of us is doing any of the duties we were hired to do. Can our employer simply change our jobs like that? Our titles and salaries remain the same but we have been expressly forbidden to perform any of the duties associated with our titles.