MADISON, Wis. -

Wisconsin Democrats are joining their rival Republicans' call for University of Wisconsin System officials to freeze tuition in light of the system's massive tuition surplus.

A Legislative Fiscal Bureau memo released last week showed the system finished the 2012 fiscal year with nearly $650 million in reserves, including $414 million in surplus tuition dollars. Republicans are questioning how the Board of Regents could justify raising tuition for six straight years when the system is so flush with cash.

Republicans have vowed to freeze tuition in the upcoming state budget.

Democratic legislative leaders, typically among the system's staunchest supports, sent a letter to system President Kevin Reilly and the board on Wednesday calling the surplus unjustifiable and asking the regents to immediately freeze tuition for two years.

A system spokesman said it's difficult to comment because the budget is still in flux.

Gov. Scott Walker said Wednesday he plans to ask Legislature to freeze tuition.