Some 40 union members demonstrated outside the hotel Wednesday calling on the Frontier to live up to terms set down by the National Labor Relations Board.
The union said the hotel owes between $5 million and $7 million in back pension contributions.
A hotel attorney disagreed, saying the Frontier has already paid $1.5 million in pension contributions.
Five unions have been on strike at the hotel since Sept. 21, 1991.
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