In the Philippine labor landscape, the distinction between "regular" and "non-regular" employment often dictates the extent of a worker's job security. However, the 1987 Constitution and the Labor Code of the Philippines establish a fundamental principle: all workers, regardless of status, are entitled to basic labor standards and due process.

1. Categorization of Non-Regular Employees

Under Article 295 (formerly 280) of the Labor Code, employees who do not meet the definition of "regular" generally fall into four categories:

Project Employees: Those whose employment has been fixed for a specific project or undertaking, the completion or termination of which has been determined at the time of engagement.
Seasonal Employees: Those who perform work that is seasonal in nature and the employment is only for the duration of the season.
Casual Employees: Those who perform work that is not usually necessary or desirable in the usual business of the employer. (Note: If a casual employee renders at least one year of service, they are considered regular for that specific activity).
Fixed-Term Employees: A category created by jurisprudence (Brent School, Inc. vs. Zamora), where employment is bound by a specific date, provided the period was agreed upon knowingly and without force.

2. Agency-Hired Employees (Tripartite Relationship)

Agency hiring involves a "tripartite" relationship between the Principal (the client company), the Contractor (the agency), and the Contractual Employee.

Legitimate Job Contracting vs. Labor-Only Contracting

The Department of Labor and Employment (DOLE) strictly regulates this through Department Order (D.O.) No. 174.

Legitimate Job Contracting: This is legal. The agency must have substantial capital (at least ₱5 million), its own equipment, and exercise control over the performance of the employees.
Labor-Only Contracting: This is prohibited. It occurs when the agency merely recruits workers for the principal and does not have substantial capital or investment. In such cases, the law bypasses the agency and considers the workers regular employees of the principal company.

3. Core Rights of Non-Regular and Agency Employees

Regardless of their status, these workers are entitled to the following statutory benefits:

Labor Standards: Minimum wage, overtime pay, night shift differential, 5 days of Service Incentive Leave (after one year of service), 13th-month pay, and holiday pay.
Social Welfare: Mandatory coverage and contributions to SSS, PhilHealth, and Pag-IBIG.
Safe Working Conditions: Compliance with Occupational Safety and Health (OSH) standards.
Self-Organization: The right to form or join a union for purposes of collective bargaining.

4. Security of Tenure and Due Process

While non-regular employees do not have "permanent" status, they enjoy security of tenure within the period or scope of their contract.

Termination for Cause: An employer cannot terminate a project or fixed-term employee before the contract ends without "Just" or "Authorized" causes (e.g., serious misconduct, retrenchment).
Procedural Due Process: If an employee is dismissed for cause, the "Twin Notice Rule" applies:
- First Notice: Detailing the grounds for termination and giving the worker a chance to explain.
- Second Notice: The final decision of the employer after considering the worker's response.
Automatic Regularization: If a project or seasonal employee's contract is repeatedly renewed for tasks vital to the employer’s business, or if a casual employee reaches one year of service, they may be legally deemed a regular employee by operation of law.

5. Liability in Agency Hiring

One of the most critical protections for agency-hired workers is Solidary Liability. Under the Labor Code, if the agency fails to pay the wages or benefits of the worker, the Principal (client company) is held jointly and severally liable as if it were the direct employer. This ensures that workers are not left without recourse if an agency disappears or files for bankruptcy.

6. The "Equal Pay for Equal Work" Principle

While not explicitly detailed as a single statute, Philippine jurisprudence and DOLE regulations lean towards parity. Agency-hired employees performing the same tasks as regular employees of the principal should not be discriminated against in terms of basic safety and dignity, though specific company-wide bonuses (not mandated by law) are often reserved for regular staff unless otherwise stipulated in a Collective Bargaining Agreement (CBA).