G.R. No. L-70763 April 30, 1987
UNITED CMC TEXTILE WORKERS UNION, petitioner, vs. THE HONORABLE LABOR ARBITER, RAYMUNDO VALENZUELA, ARBITRATION BRANCH, NATIONAL LABOR RELATIONS COMMISSION, respondents.

FACTS

Petitioner union filed a complaint against Central Textile Mills, Inc. (CTMI) for non-payment of the 1978 Christmas bonus as stipulated in their collective bargaining agreement (CBA). The Labor Arbiter ruled in favor of the union, ordering CTMI to pay P122,840.00. The NLRC affirmed the decision with a minor modification for verification of claims. CTMI’s petition for certiorari to the Supreme Court (G.R. No. 58666) was dismissed for lack of merit on January 20, 1982, and this dismissal became final and executory on September 22, 1982, upon entry of judgment.
When the union moved for execution in 1984, CTMI argued the decision had become moot and academic due to the Supreme Court’s subsequent ruling in National Federation of Sugar Workers vs. Central Azucarera de la Carlota (the La Carlota doctrine), which held that employers already paying a Christmas bonus equivalent to the 13th-month pay are not obligated to pay an additional 13th-month pay under P.D. No. 851. The Labor Arbiter refused to proceed with execution, prompting the union to file this petition for mandamus to compel the issuance of the writ.

ISSUE

Whether the public respondent Labor Arbiter can refuse to execute a final and executory judgment of the Supreme Court on the ground that a subsequent judicial ruling has rendered it moot and academic.

RULING

The Supreme Court granted the petition and ordered the Labor Arbiter to issue the writ of execution. The Court held that a final and executory judgment can no longer be altered, amended, or modified, and must be executed as a matter of right. This is the immutable doctrine known as “the law of the case.” The La Carlota ruling, promulgated later, cannot retroactively nullify a judgment that has already attained finality. The Court emphasized that it had already dismissed CTMI’s petition in G.R. No. 58666 and denied its motion for reconsideration after the La Carlota decision was issued, demonstrating a deliberate choice not to apply the new doctrine to this specific case.
Furthermore, the Court found the Christmas bonus under the 1978 CBA was a separate contractual obligation distinct from the statutory 13th-month pay. The CBA’s graduated bonus based on length of service served a different purpose—rewarding seniority—not contemplated by P.D. No. 851. The fact that the bonus provision was deleted in a subsequent 1983 CBA did not extinguish the vested right to the 1978 bonus under the prior agreement. Therefore, the final judgment ordering its payment must be enforced.