Short answer. Yes. Substituting or altering an employment contract that was approved and verified by the labour department, without the Secretary's approval, is a prohibited practice. The ban runs from the moment the parties actually sign and continues through the whole life of the contract.
What the law says
To substitute or alter employment contracts approved and verified by the Department of Labor from the time of actual signing thereof by the parties up to and including the periods of expiration of the same without the approval of the Secretary of Labor
Labor Code, Article 34 — Prohibited Recruitment Practices. Read the full provision →
The verified contract is the one that counts
The prohibition covers substituting or altering contracts approved and verified by the Department of Labor, and it runs from the time of actual signing thereof by the parties up to and including the periods of expiration of the same. Two consequences follow. The protection does not lapse the moment you board the plane — it covers the whole term, so a replacement produced in month six is as much within the clause as one produced at the airport. And it is aimed at alteration as well as wholesale substitution: cutting the salary figure in the verified contract is covered even if everything else stays.
Signing the second contract does not fix the problem
This is the assumption most workers arrive with, and it is the one worth correcting. The clause carves out no exception for a substitution the worker consented to. The approval it asks for is the approval of the Secretary of Labor — the government's, not yours, and a worker cannot supply it by signing. A worker standing in a foreign airport, passport in someone else's hand and no return ticket, is not in a position to refuse, and the provision is written on that understanding. Your signature on the replacement is a fact to explain, not a bar to complaining.
What the substitution usually changes
Pay is the common one, but look at the whole document. Position and duties are often quietly downgraded, the term lengthened, rest days removed, deductions introduced, and the governing law or the forum for disputes changed. Compare the two papers line by line rather than reading only the salary. A difference in the job title can matter as much as the money, because it is often what the lower pay is later justified by.
What to keep, starting now
Hold on to the verified contract signed in the Philippines — the copy bearing the verification — and to the replacement, even a photograph of it taken quickly. Keep your payslips or a note of what you were actually paid and when, and the messages in which the change was explained or demanded. Store copies somewhere your employer cannot reach. The case against the agency that deployed you is normally built on the gap between the two documents, so the documents are the priority.