I think it is fair to tell a potential employer that you felt you were undercompensated at your last position. But that comes with a significant precondition: you better really be good or they better have been genuinely undercompensating you. A great hiring manager will easily be able to tell which was the case based on what you tell them.

There are some employees who never feel they are sufficiently compensated, but they are actually not the stars they believe themselves to be. Then there are those who are genuine stars, are carrying the company on their back and are undercompensated (and underappreciated). If you are in the latter group, be prepared to make your case to a new employer. If you can point directly to customer wins, revenue and margin created, etc. and make a solid pitch for your talents then you should be fine. That would simply be a great talent getting paid what he is worth. It will greatly bolster your case if you have a reference who can vouch for your capabilities and accomplishments at your last company. If you cannot make a great case for your value, you will have a much tougher time - especially in this economic environment.

One more suggestion would be to approach the subject humbly and always armed with and speaking from the facts. As a repeat CFO and COO I have had many compensation discussions with salespeople and sales leaders, and they never thought they were getting paid what they were worth. However, those armed with the facts and rational arguments, delivered in a non-threatening way, always got more buy-in from both the CEO and I. I would use that same approach with a recruiter or hiring manager. Good luck out there.