Popular characterizations of trade union preferences assume that the i
ncome of laid-off union members is exogenous. Given the widespread exi
stence of (partial) intra-union distribution schemes including severan
ce pay, this paper provides a model of union-firm bargaining in which
workers' layoff income is endogenously determined. Where unions and fi
rms bargain over wages and severance pay, workers' incomes are invaria
nt to their employment status, and the wage corresponding to the level
of ex post employment is equal to the opportunity cost of labour. The
equality of marginal productivity to the opportunity cost of labour (
which is a necessary and sufficient condition for the bargaining surpl
us to be maximized) characterizes employment in both the right-to-mana
ge and the efficient bargaining union models, and has implications for
empirical research trying to distinguish between these two approaches
. The bargaining model developed in this paper can also be compared wi
th the outcome of the implicit contract model with redundancy pay; but
a crucial point of difference is that the result in this paper derive
s from a unionized labour market where unions and firms bargain over w
ages and redundancy pay, while the implicit contract result derives fr
om a perfectly competitive labour market in which competitive forces l
ead to an efficient outcome.