In this paper, we combine a monopolistic model à la Dixit and Stiglitz and a matching model derived from Pissarides (2000) in the case of large firms. As in Cahuc and Wasmer (2001), we consider an intra firm bargaining model for the wage determination. Moreover, we allow for increasing returns to scale in the aggregate production function leading to multiple equilibria existence. Finally, based on economy dynamics study and numerical simulations, we show how the dynamical properties are altered in the case of multiple equilibria compared to the one of unique equilibrium and illustrate the issues of economic policy design in the case of multiple equilibria.