Short answer. The secretary or the treasurer certifies under oath, and the president attests. Article 235 requires all requisite documents and papers to be certified under oath by the secretary or the treasurer, as the case may be, and attested to by the president of the organisation.
What the law says
All requisite documents and papers shall be certified under oath by the secretary or the treasurer of the organization, as the case may be, and attested to by its president.
Labor Code, Article 235 — Action On Application. Read the full provision →
Two signatures, two different acts
Article 235 provides that All requisite documents and papers shall be certified under oath by the secretary or the treasurer of the organization, as the case may be, and attested to by its president. These are not duplicates of one another. The certification is made under oath, which means it is sworn, and it comes from the officer who holds the record being submitted. The attestation by the president is the organisation's own confirmation that the paper is what it purports to be. A set of documents signed only by the president has not satisfied the first half of the sentence.
Which of the two officers certifies what
The phrase as the case may be tells you the choice is not arbitrary. The officer who certifies is the one whose office the document belongs to. Minutes, the constitution and by-laws, resolutions and the list of members are the secretary's records. Financial statements and anything about dues, funds or accounts are the treasurer's. Matching each document to the officer who actually keeps it is the sensible reading, and it avoids the awkwardness of a treasurer swearing to the accuracy of minutes nobody says he took.
Certified under oath means sworn, not merely signed
An oath requires the certifying officer to appear before a person authorised to administer it, and to swear to the document there. A signature added at a meeting, however sincerely, is not that. This is also why the officers should read what they are certifying rather than signing a stack presented to them — the oath is personal to the officer who takes it, and it is made about the truth of the contents. Keep a complete signed and sworn copy of everything filed.
Getting it right the first time saves the clock
Defective execution is the ordinary reason an application is returned, and every return costs a new union weeks it can ill afford. Before filing, confirm that the persons signing actually hold the offices claimed and that your records show their election, that each document is certified by the right officer, that the oath was properly taken, and that the president has attested to the set. The same article obliges the Bureau to act within thirty days from filing, so a clean submission is what starts that period running in earnest.