All workers, all employees may organize from 1st day of work

All persons employed in commercial, industrial and agricultural enterprises and in religious, charitable, medical, or educational institutions, whether operating for profit or not, shall have the right to self-organization and to form, join, or assist labor organizations of their own choosing for purposes of collective bargaining.

Ambulant, intermittent, and itinerant workers, self-employed people, rural workers and those without any definite employers may form labor organizations for their mutual aid and protection. [Art. 253] Any employee, whether employed for a definite period or not, shall, beginning on his first day of service, be considered as an employee for purposes of membership in any labor union. [Art. 292(c)]

Employee includes […] any individual whose work has ceased as a result of or in connection with any current labor dispute or because of any unfair labor practice if he has not obtained any other substantially equivalent and regular employment. [Book V, Rule I, Sec. 1(f)]

Employees of non-profit organizations are now permitted to form, organize or join labor unions of their choice for purposes of collective [FEU-Dr. Nicanor Reyes Medical Foundation Inc. v. Trajano, G.R. No. 76273 (1992)]