A veto, in the context of non-monogamy, is the agreement that one partner can require another to end an outside relationship. It is usually written into the early architecture of an opening marriage as a safety device — the reassurance that the primary bond will not be destroyed by something new. People reach for it for the same reason they reach for a fire extinguisher: they hope they will never use it, but they want to know it is there. The phrase that gets used is "veto power," and the borrowing from parliamentary language is not accidental. It frames the relationship as a small legislature where one member can halt a motion. That framing reveals both the appeal and the trouble.
The appeal is obvious. If you are stepping off the cliff of monogamy and your stomach is in your throat, a veto is a rope tied to a tree. It lets you say to your partner, "Go ahead. Date. Fall in love a little. But if it threatens us, I can pull this cord." For many couples, the veto is what makes the opening possible at all. Without it the fear is too loud to hear anything else. Polyamorous writers from Easton and Hardy onward have acknowledged this transitional usefulness even as they have warned about its costs. The veto is training wheels. The question is whether you ever take them off, and what damage they do if you do not.
The trouble is that a veto is, almost by definition, an instrument used against someone who has no voice in the decision. Your partner's new lover — call them the third — was not in the room when the rule was written. They will not be in the room when it is invoked. They learn about their own dismissal through the partner they have grown to love, who turns out to be governed by a treaty negotiated before they existed. Franklin Veaux and Eve Rickert call this the asymmetry of "couple privilege," and it is the structural critique that has driven most thoughtful poly communities away from hard vetoes over the last fifteen years. A veto treats the third as a guest in someone else's house, with eviction rights reserved for the original residents.
The defense is that all relationships have implicit vetoes. If your spouse tells you the new boyfriend is making them miserable, you will probably break up with him, agreement or no agreement. True. But the difference between a soft request and a coded contract is the difference between negotiation and authority. A request invites response. A veto forecloses it. When the veto exists as a named power, the partner using it does not have to do the harder work of articulating what is actually wrong — the jealousy, the time imbalance, the specific behavior of the third, the fear of being replaced. They can just press the button. The other partner then has to choose between obedience and rebellion, with no middle path of dialogue. The thing that was supposed to protect the relationship corrodes it instead.
There is also the question of who gets vetoed. Studies of long-term polyamorous households, including Sheff's longitudinal work, show that vetoes are used disproportionately against newer, less established, and structurally weaker partners — almost never against the primary's career, family, or close friends. The veto is rarely deployed against an objectively dangerous person. It is deployed against the person who is becoming too important too fast, which is to say, against love. That is a bad use of power. It teaches the vetoing partner that comfort can be purchased by truncating someone else's connection, and it teaches the vetoed partner that their love is provisional on the moods of a stranger.
The middle path, which most experienced poly writers now recommend, is to replace the veto with what they call a "voice" or a "concern process." Either partner can raise any concern about any relationship at any time, and the other partner is obligated to listen, investigate, and respond — but the decision about whether to continue the outside relationship remains with the person inside it. This is harder. It requires more talking, more sitting with discomfort, more trust that your partner will not let you drown even when they are not bound by a clause. But it produces relationships in which everyone has standing, including the third. The veto promises safety through hierarchy. The voice offers safety through being heard. They are not the same and over time the difference becomes the marriage.