Short answer. At least ten. Article 237 requires a federation or national union applying for registration to submit proof of the affiliation of at least ten locals or chapters, each of which must be a duly recognised collective bargaining agent in the establishment or industry where it operates.
What the law says
Proof of the affiliation of at least ten (10) locals or chapters, each of which must be a duly recognized collective bargaining agent in the establishment or industry in which it operates, supporting the registration of such applicant federation or national union
Labor Code, Article 237 — Requirements For Federations. Read the full provision →
Ten, and each of them must already be a bargaining agent
The number is the part everyone remembers, but the qualifier is what applications founder on. The article asks for Proof of the affiliation of at least ten (10) locals or chapters, each of which must be a duly recognized collective bargaining agent in the establishment or industry in which it operates, supporting the registration of such applicant federation or national union. So a count of ten affiliated groups is not enough. Each one has to be the recognised bargaining agent where it operates, and each has to be supporting this particular application.
Why the requirement is set that high
A federation is not simply a larger union; it speaks for organisations that already represent workers, and its registration carries weight across many workplaces at once. Requiring ten established bargaining agents is a test of whether the applicant genuinely federates existing unions rather than assembling nominal affiliates for the purpose of the application. It also means a federation's standing rests on organisations that have themselves already been chosen by workers in their own establishments.
The second requirement is a map of the federation
Alongside the proof of affiliation, the article calls for the names and addresses of the companies where the locals or chapters operate and the list of all the members in each company involved. Read together, the two paragraphs ask the applicant to show not just that it has ten affiliates but where they are and who is in them. Assembling that material takes real coordination with each local, and it is worth starting well before the application is drafted, since membership lists have to come from the locals themselves.
What to have in order before filing
For each affiliate, you will want the document showing it is the recognised bargaining agent in its establishment or industry, the resolution or instrument of affiliation, and its support for this registration. Then the company names and addresses and the member lists for each. These sit on top of the requirements the preceding articles impose on any applicant, including the certification under oath by the secretary or treasurer and the attestation by the president. A set that is short by one qualified affiliate is not a near miss; it does not meet the article.