Mutuality of Contracts: When Banks Cannot Unilaterally Change Interest Rates

The principle of mutuality of contracts is a cornerstone of Philippine civil law. It ensures that both parties to a contract are bound by its terms, and that its performance cannot be left to the whims of just one side. In the 2019 case of Vasquez v. Philippine National Bank (G.R. No. 228355), the Supreme Court applied this principle squarely to banking practice, ruling that a bank cannot unilaterally change interest rates on a loan without the borrower's consent. The decision is a critical reminder for both lenders and borrowers about the limits of contractual freedom in loan agreements.

The Facts of the Case

In 1996, Engr. Ricardo Vasquez obtained two loans from the Philippine National Bank (PNB): P600,000 under the Pangkabuhayan ng Bayan Program and P800,000 under a Revolving Credit Line. Both loans were secured by a real estate mortgage over four parcels of land in Cavite.

The loan documents did not fix a definite interest rate. Instead, the Credit Agreement stated that interest would be charged at "Prime Rate plus Spread," without defining how that rate would be computed. The promissory notes merely referred to the "applicable" interest rate. Crucially, the Credit Agreement also contained provisions allowing PNB to increase or decrease interest rates "depending on whatever policy the Bank may adopt in the future" and declared the bank's computation of interest as "conclusive and binding" on the borrower.

Over time, PNB applied varying interest rates on Vasquez's loans—from 16% up to 33% on one loan, and from 34% down to 20.189% on the other. PNB admitted during trial that it sent no notices of escalation to Vasquez before applying these changes. When Vasquez defaulted, PNB foreclosed on his properties.

The Issue

The central question before the Supreme Court was whether PNB's interest rate scheme—which allowed it to unilaterally modify rates based on its own future policies—was valid under Philippine law.

The Ruling: Unilateral Rate Changes Are Void

The Supreme Court ruled against PNB, declaring the interest rate scheme null and void for violating the principle of mutuality of contracts.

Article 1308 of the Civil Code provides that a contract "must bind both contracting parties; its validity or compliance cannot be left to the will of one of them." The Court explained that this principle is violated when the determination or imposition of interest rates is left to the sole discretion of one party.

The Court found that PNB's scheme was not a valid "floating rate" system. Under the Bangko Sentral ng Pilipinas' Manual of Regulations for Banks, floating rates must be based on market-based reference rates—such as Manila Reference Rates or T-Bill rates—plus an agreed margin. These reference rates must be stated in writing and agreed upon by the parties. PNB's loan documents contained no such market-based reference; instead, the rates depended entirely on PNB's own future policies.

The Court also clarified that not all escalation clauses are invalid. Escalation clauses are acceptable when anchored on reasonable and valid standards. Here, however, the increases were "solely potestative" on PNB's part—that is, dependent entirely on the bank's will—making them void.

The Effect on Foreclosure

Because the interest rates were void, the Court held that Vasquez was not in default. Under Article 1252 of the Civil Code, if a debt produces interest, payment of the principal is not deemed made until the interest is covered. Since the interest obligations were illegal and non-demandable, the principal obligation was likewise not yet demandable. Consequently, PNB should not have foreclosed on the properties.

The Court cited prior jurisprudence holding that when a debtor is not given the opportunity to settle the correct amount due because of void interest rates, foreclosure proceedings cannot be instituted, and the registration of such a sale is invalid.

Practical Takeaways

• Banks cannot unilaterally change interest rates. Any modification to the interest rate in a loan agreement must be mutually agreed upon by both parties. A provision allowing the bank to adjust rates based on its own future policies is void.
• Floating rates must have a clear basis. A valid floating rate system must reference an objective, market-based rate (like T-Bill rates) stated in writing and agreed upon by the parties. A vague "prime rate plus spread" without defined parameters is not enough.
• Escalation clauses are not automatically void. They are valid when based on reasonable and valid grounds, not solely on the lender's discretion.
• Borrowers should check their loan documents. If a loan agreement leaves interest rates open-ended or grants the bank broad discretion to change rates, that provision may be unenforceable.
• Foreclosure based on void interest rates may be challenged. If a borrower was not given the chance to pay the correct amount because of unlawful interest impositions, the foreclosure and its registration may be invalidated.

This article is general information and not legal advice. For your specific situation, consult a lawyer or ask ASG Legal AI.