We investigate the role of non-separable preferences on the occurrence of macroeconomic instability under a balanced-budget rule where government spending is financed by a tax on labor income. Considering a one-sector neoclassical growth model with a large class of non-separable utility functions, we find that expectations-driven fluctuations easily occur when consumption and labor are Edgeworth substitutes or weak Edgeworth complements. Under these properties, an intermediate range of tax rates and a sufficiently low elasticity of intertemporal substitution in consumption lead to instability.