Short answer. An employee is casual only if the work is not usually necessary or desirable to the employer's usual business, and does not fall under a specific project or seasonal exception. Even then, Article 280 makes an employee regular anyway, as to that activity, once they have rendered at least one year of service, continuous or broken.
What the law says
an employment shall be deemed to be regular where the employee has been engaged to perform activities which are usually necessary or desirable in the usual business or trade of the employer, except where the employment has been fixed for a specific project or undertaking the completion or termination of which has been determined at the time of the engagement of the employee or where the work or service to be performed is seasonal in nature and the employment is for the duration of the season. An employment shall be deemed to be casual if it is not covered by the preceding paragraph: Provided, That any employee who has rendered at least one year of service, whether such service is continuous or broken, shall be considered a regular employee with respect to the activity in which he is employed and his employment shall continue while such activity exists.
Labor Code, Article 280 — Regular And Casual Employment. Read the full provision →
Regular status starts with the nature of the work
Article 280 defines regular employment first, and casual employment by what is left over. Employment is regular where the employee performs activities which are usually necessary or desirable in the usual business or trade of the employer. That is a description of the work itself — is it the kind of activity the employer's business ordinarily needs — rather than of the contract's label or the employee's job title.
Two named exceptions to that rule
Even work that is necessary or desirable to the business does not make an employee regular if it fits one of two exceptions the article carves out: a specific project or undertaking whose completion or termination was already fixed at the time the employee was engaged, or work that is seasonal in nature, where the employment lasts for the duration of that season. These two categories are treated differently from ordinary regular work even though the activity itself may otherwise be necessary to the business.
Casual is defined as everything else
Article 280 defines casual employment negatively: an employment shall be deemed to be casual if it is not covered by the preceding paragraph. In other words, casual status is not a separate, independently defined category — it is simply what remains once employment that qualifies as regular, project-based, or seasonal has been set aside. Whether a given engagement is casual depends entirely on it failing to meet the regular-employment test first.
The one-year proviso overrides the casual label
The article does not let casual status last indefinitely. It provides that any employee who has rendered at least one year of service, whether such service is continuous or broken, shall be considered a regular employee with respect to the activity in which he is employed. Once that year is reached, the employee becomes regular as to that specific activity, and the employment continues for as long as the activity itself still exists — regardless of how the engagement was originally labeled.