It is commonly argued that the successful stabilisation of asymmetric shocks in a monetary union requires, either flexible wages and/or labour mobility, absent inter-regional fiscal transfer payments. The current pattern of relative wage rigidity and labour inertia in Europe is thus viewed by many observers as a problematic factor in the successful functioning of the European common currency area. We investigate in the context of some historical case studies whether monetary integration can bring about a regime shift in the degree of labour market flexibility. Specifically, we employ econometric methods to test whether the onset of monetary union in the US and the Gold Standard in selected countries have rendered real wages more procyclical. Previously entitled: 'The Endogeneity of Optimum Currency Area Criteria in Historical Perspective - Some Lessons for European Monetary Union (EMU)' We find and qualify suggestive evidence from our empirical exercise that indeed a Lucas Critique argument applies so that monetary unions and credibly fixed exchange rate regimes in general might induce wages to carry the burden of macroeconomic adjustment in lieu of independent monetary policy and/or fiscal transfers. We argue that economic theory should borrow a leaf from the book of economic history and - rather than treating wage formation as exogenous - we consider the degree of real wage flexibility to depend upon the nature of the monetary policy regime. We conclude by relating our findings to the European Monetary Union (EMU).