They are protesting at the decision by the receiver to stop manufacturing and make 480 staff redundant.
The company, which employs 670 people, went into receivership at the beginning of January.
The trade union Unite said there are two potential purchasers of the business.
A statement by the receiver, David Carson of Deloitte Ireland, said: "The decision to cease manufacturing does not necessarily preclude a resumption of operations in Waterford in the future.
"The receiver is continuing negotiations with interested parties with a view to a sale of the company's assets and those discussions are focused on agreeing the terms upon which a transaction could be completed."
The employees say they will not leave the plant until they meet Mr Carson.
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