Principle M: In the absence of special justification, it is not permissible for one person, A, in order to get another person, B, to do some act, X (which A wants B to do and which B is morally free to do or not do but would otherwise not do), to lead B to expect that if he or she does X then A will do Y (which B wants but believes that A will otherwise not do), when in fact A has no intention of doing Y if B does X, and A can reasonably foreseen that B will suffer signficant loss if he or she does X and A does not reciprocate by doing Y.

Scanlon What we Owe ... p.298