Millares was dismissed for allegedly having "abandoned" his post; and petitioner Lagda, for his alleged "unavailability for contractual sea service." However, that petitioners did not abandon their jobs such as to justify the unlawful termination of their employment is borne out by the records. To constitute abandonment, two elements must concur: (1) the failure to report for work or absence without valid or justifiable reason; and (2) a clear intention to sever the employer-employee relationship, with the second element as the more determinative factor and being manifested by some overt acts. Mere absence is not sufficient. It is the employer who has the burden of proof to show a deliberate and unjustified refusal of the employee to resume his employment without any intention of returning. 21[21] In this case, private respondents failed to discharge this burden. They did not adduce any proof of some overt act of the petitioners that clearly and unequivocally show their intention to abandon their posts. On the contrary, the petitioners lost no time in filing the case for illegal dismissal against private respondents, taking them only about a month from the time their termination became effective on September 1, 1989 to the filing of their complaint on October 5, 1989. They cannot, by any reasoning, be said to have abandoned their work, for as we have also previously ruled, the filing by an employee of a complaint for illegal dismissal is proof enough of his desire to return to work, thus negating the employers charge of abandonment.22[22] Mani kx Furthermore, the absence of petitioners was justified by the fact that they secured the approval of private respondents to take a leave of absence after the termination of their last contracts of enlistment. Subsequently, petitioners sought for extensions of their respective leaves of absence. Granting arguendo that their subsequent requests for extensions were not approved, it cannot be said that petitioners were unavailable or had abandoned their work when they failed to report back for assignment as they were still questioning the denial of private respondents of their desire to avail of the optional early retirement policy, which they believed in good faith to exist. Clearly, petitioners termination is illegal. Thus, under Article 27923[23] of the Labor Code, petitioners are entitled to reinstatement without loss of seniority rights and other 21[21] Artemio Labor, et. al. vs. NLRC and Gold City Commercial Complex, Inc., and Rudy Uy, 248 SCRA 183 (1995) 22[22] Id., at 198. 23[23] Art. 279. Security of Tenure. - In cases of regular employment, the employer shall not terminate the services of an employee except for just cause or when authorized by this Title. An employee who is unjustly dismissed from work shall be entitled to reinstatement without loss of seniority rights and other privileges and to his full backwages, inclusive of allowances, and to his other benefits or their monetary equivalent computed from the time his compensation was withheld from him up to the time of his actual reinstatement.