A general equilibrium model of heterogeneous capital is employed to investigate whether, how and to what extent monetary policy and market structure may have contributed to the decline of the labor share in the U.S. in recent decades. By construction the model allows monetary policy to affect the labor share through two channels, i.e. one linking the policy rate to the real interest rate and another linking the latter to the useful life of producers’ goods, whereas regarding market structure, the more competitive the economy, the higher the labor share. From its solution using U.S. data over the period 2000–2014 it emerges that the persistent reduction in the policy rate on the one hand slowed down the decline in the labor share and on the other accelerated it, because the reduction in the policy rate was accompanied by a robust upward trend in the equilibrium real rate of interest, which increased the useful life of producers’ goods. In turn, to gauge the relative strength of these two opposite effects, the equation of the labor share is estimated by means of the autoregressive distributed lag method. The results show that the adverse effect of monetary policy through the useful life of producers’ goods was more than 12 times as strong as the favorable effect of the policy rate and on this ground I conclude that the monetary policy contributed to the decline of the labor share significantly, at least since 2000. As for the market structure, it is found that even if firms had and attempted to exercise monopoly power, it would be exceedingly difficult to exploit it because the demand of consumers’ goods is significantly price elastic.