Should a subset of member states of a federation be allowed to form a sub-union on some policy issue? When centralization is not politically feasible, allowing an enhanced cooperation agreement among a subset of countries permits the latter to gain benefits which would otherwise be lost....

We develop a two-country, two-sector model with a continuum of workers to address the link between migration and trade where policy is determined by a simple referendum. In particular, we address two questions. First, are states already in free trade areas more likely to support full integration...