Proper Venue Section 1(a) of Rule IV of the NLRC Rules of Procedure reads: "Section 1. Venue – (a) All cases which Labor Arbiters have authority to hear and decide may be filed in the Regional Arbitration Branch having jurisdiction over the workplace of the complainant/petitioner; Provided, however that cases of Overseas Filipino Worker (OFW) shall be filed before the Regional Arbitration Branch where the complainant resides or where the principal office of the respondent/employer is situated, at the option of the complainant. "For purposes of venue, workplace shall be understood as the place or locality where the employee is regularly assigned when the cause of action arose. It shall include the place where the employee is supposed to report back after a temporary detail, assignment or travel. In the case of field employees, as well as ambulant or itinerant workers, their workplace is where they are regularly assigned, or where they are supposed to regularly receive their salaries/wages or work instructions from, and report the results of their assignment to their employers." Under the "Migrant Workers and Overseas Filipinos Act of 1995" (RA 8042), a migrant worker "refers to a person who is to be engaged, is engaged or has been engaged in a remunerated activity in a state of which he or she is not a legal resident; to be used interchangeably with overseas Filipino worker."21 Undeniably, respondent was employed by petitioner in its branch office in Singapore. Admittedly, she is a Filipino and not a legal resident of that state. She thus falls within the category of "migrant worker" or "overseas Filipino worker." As such, it is her option to choose the venue of her Complaint against petitioner for illegal dismissal. The law gives her two choices: (1) at the Regional Arbitration Branch (RAB) where she resides or (2) at the RAB where the principal office of her employer is situated. Since her dismissal by petitioner, respondent has returned to the Philippines -- specifically to her residence at Filinvest II, Quezon City. Thus, in filing her Complaint before the RAB office in Quezon City, she has made a valid choice of proper venue. Third Issue: Illegal Dismissal The appellate court was correct in holding that respondent was already a regular employee at the time of her dismissal, because her three-month probationary period of employment had already ended. This ruling is in accordance with Article 281 of the Labor Code: "An employee who is allowed to work after a probationary period shall be considered a regular employee." Indeed, petitioner recognized respondent as such at the time it dismissed her, by giving her one month’s salary in lieu of a one-month notice, consistent with provision No. 6 of her employment Contract. Notice and Hearing Not Complied With As a regular employee, respondent was entitled to all rights, benefits and privileges provided under our labor laws. One of her fundamental rights is that she may not be dismissed without due process of law. The twin requirements of notice and hearing constitute the essential elements of procedural due process, and neither of these elements can be eliminated without running afoul of the constitutional guarantee. 22 In dismissing employees, the employer must furnish them two written notices: 1) one to apprise them of the particular acts or omissions for which their dismissal is sought; and 2) the other to inform them of the decision to dismiss them. As to the requirement of a hearing, its essence lies simply in the opportunity to be heard.23 The evidence in this case is crystal-clear. Respondent was not notified of the specific act or omission for which her dismissal was being sought. Neither was she given any chance to be heard, as required by law. At any rate, even if she were given the opportunity to be heard, she could not have defended herself effectively, for she knew no cause to answer to. All that petitioner tendered to respondent was a notice of her employment termination effective the very same day, together with the equivalent of a one-month pay. This Court has already held that nothing in the law gives an employer the option to substitute the required prior notice and opportunity to be heard with the mere payment of 30 days’ salary.24 Well-settled is the rule that the employer shall be sanctioned for noncompliance with the requirements of, or for failure to observe, due process that must be observed in dismissing an employee.25 No Valid Cause for Dismissal Moreover, Articles 282,26 28327 and 28428 of the Labor Code provide the valid grounds or causes for an employee’s dismissal. The employer has the burden of proving that it was done for any of those just or authorized causes. The failure to discharge this burden means that the dismissal was not justified, and that the employee is entitled to reinstatement and back wages. 29 Notably, petitioner has not asserted any of the grounds provided by law as a valid reason for terminating the employment of respondent. It merely insists that her dismissal was validly effected pursuant to the provisions of her employment Contract, which she had voluntarily agreed to be bound to. Truly, the contracting parties may establish such stipulations, clauses, terms and conditions as they want, and their agreement would have the force of law between them. However, petitioner overlooks the qualification that those terms and conditions agreed upon must not be contrary to law, morals, customs, public policy or public order.30 As explained earlier, the employment Contract between petitioner and respondent is governed by Philippine labor laws. Hence, the stipulations, clauses, and terms and conditions of the Contract must not contravene our labor law provisions.