With the Defense Department set to lay out  a final furlough policy today,  the Merit Systems Protection Board has rejected a union’s request for a heads-up on  how it could decide appeals from employees who challenge the decision to force them to take unpaid time off. “Under federal law, the Board is prohibited from issuing advisory opinions,” the agency’s clerk, William Spencer, said in a letter yesterday to Gregory Junemann, president of the International Federation of Professional and Technical Engineers that cites the relevant provision of federal law.  This afternoon, Defense Secretary Chuck Hagel is expected to officially tell DoD…