On December 28, 1982 respondent Associated Labor Unions (ALU), for and in behalf of all the rank-and-file workers and employees of petitioner, filed a complaint before the Ministry of Labor and Employment, Davao City, against petitioner, for "Payment of the Thirteenth-Month Pay Differentials." Respondent ALU sought to recover from petitioner the thirteenth month pay differential for 1982 of its rank-and- file employees, equivalent to their sick, vacation and maternity leaves, premium for work done on rest days and special holidays, and pay for regular holidays which petitioner, allegedly in disregard of company practice since 1975, excluded from the computation of the thirteenth month pay for 1982. In its answer, petitioner claimed that it erroneously included items subject of the complaint in the computation of the thirteenth month pay for the years prior to 1982, upon a doubtful and difficult question of law. 1. Are payments for sick, vacation and maternity leaves, premiums for work done on rest days and special holidays, and pay for regular holidays included in the computation and payment of thirteenth month pay?