KELLOGG, Idaho Sunshine Mining Co.'s threat to close its silver mine if a new labor contract is not hammered out has been made so many times it's hollow, a union representative said Thursday.

''I would say its a really stale threat that's been going on for the last four years,'' said Steve Brown, a spokesman for the United Steelworkers of America.

The mine could be closed if the union does not accept management's offer by May 31, said Don Hullinger, a spokesman for Sunshine Precious Metals, Inc., a subsidiary of the Dallas-based Sunshine Mining Co.

The company also announced several weeks ago that it plans to lay off 300 of 425 employees June 1 because of depressed silver prices.

''Without an agreement, do we keep operating on a smaller scale, or simply shut down the mine completely?'' Hullinger said, adding that no decision had been made.

Members of Local 5089 on Saturday rejected by a 2-to-1 margin the 3-year contract offered by the company. The proposed pact would have required them to pay $15 a month for health insurance. Workers' premiums now are fully paid by the company.

Negotiations began in February. The contract expired April 27.

''I'm hoping we can get back to (the) bargaining table before the end of the month,'' Brown said. ''But the miners don't want to be the first in the valley to have to pay for medical insurance.''