The Trump administration has telegraphed that mass firings are coming, but officials have cautioned that such moves could violate appropriations law.Senior federal officials have quietly counseled several agencies against firing employees while the government is shut down — as President Donald Trump has suggested he will — warning the strategy may violate appropriations law, according to two people familiar with the matter who spoke on the condition of anonymity to discuss sensitive internal deliberations. The officials cautioned that firings — known as RIFs, or reductions in force — could be vulnerable to legal challenges under statutes labor unions cited this...