Short answer. No. Article 1212 of the Civil Code draws a clear line: a solidary creditor may act unilaterally only when what he does is useful to the others. Anything that would be prejudicial to the other creditors he cannot do on his own — the law forbids it.
What the law says
Each one of the solidary creditors may do whatever may be useful to the others, but not anything which may be prejudicial to the latter.
Civil Code, Article 1212 — Useful and Prejudicial Acts of a Solidary Creditor. Read the full provision →
The rule in plain terms
When two or more people are creditors in a solidary obligation, each of them holds the entire credit but they all share an interest in it. Article 1212 governs what any one of them can do alone. The rule is simple: useful acts are allowed; prejudicial acts are not. A solidary creditor who acts in a way that benefits the group — collecting what is owed, preserving the obligation, taking steps to prevent prescription — does so within the law. One who acts in a way that diminishes what the others are entitled to does not.
What counts as prejudicial
An act is prejudicial when it reduces or extinguishes what the other creditors would otherwise recover. The clearest example is a remission or condonation of the debt given by one solidary creditor without the others' consent — that act would wipe out, at least in part, what the remaining creditors had a right to demand. It is precisely this kind of unilateral act that Article 1212 bars. The concern is that solidarity among creditors is meant to be a collective advantage, not a mechanism that lets one member quietly undercut the rest.
Who is bound by this rule
Article 1212 binds every solidary creditor — there is no exception for the creditor who happens to hold the largest share, the one who is most senior, or the one who managed the original transaction. The rule operates equally across all of them. It also does not distinguish between active and passive conduct: whether the prejudicial act is a deliberate remission or a settlement entered into without telling the others, the same prohibition applies. The solidary arrangement gives each creditor power to act for the group; it does not give any one of them power to act against the group.
Why this matters if you are one of the creditors
If you are one of several creditors in a solidary arrangement and you discover that a co-creditor has already negotiated a partial settlement, granted the debtor an extension, or forgiven part of the debt without your agreement, Article 1212 is the provision most directly on point. Whether that act can still be undone or whether you are entitled to compensation from the co-creditor who acted improperly depends on the specific facts and what was actually agreed. The article establishes the legal standard; your remedies flow from there. Legal advice specific to your situation is the right next step.