Economists identify several types of unemployment, including classical, structural and demand deficient unemployment.
Classical unemployment relates to the effect of a sustained increase in real wages above the free market equilibrium.
Classical unemployment could arise when free markets are prevented from establishing a market clearing equilibrium, including:
An increase in real wages will affect both the demand for, and supply of labour.
An increase in real wages (at W1) will cause the demand for labour to contract (a to b) and the supply to extend (a to c). This is the Classical theory of unemployment - if real wages rise above the market rate, fewer will be employed, though more will look for work.
A minimum wage would cause Classical unemployment if set above the market rate.
The extent of Classical unemployment depends up elasticity of demand for labour, and on the elasticity of supply of labour. With a more elastic supply of labour as a result of lower skills or fewer barriers to entry, the impact of higher wages is significant in encouraging low skilled workers to join the labour market, hence increasing Classical unemployment. Also, if demand for labour is elastic, perhaps due to the ease with which capital can be substituted for labour, the contraction of demand may have a significant effect on the amount of surplus labour created.
Critics of this theory suggest that if we follow the logic then it can be argued that reducing unemployment can be successfully achieved by reducing wages back to the theoretical market clearing rate.
However, there are at least two objections to this:
Free markets do not always arrive at the socially optimal level of employment and wages, such as where monopsonists are free to set low wages and employment, or where imperfect information exists in the labour market.
Finally, market forces do not necessarily operate in the public sector, where wages are set by government or government controlled pay-settlement organisations. In other words there is not an equivalent free market equilibrium wage rate against which to make a comparison.