The employer is called a monopsonist

The employer faces an upward sloping supply curve for labour, which is also the average cost of labour, ACL

The employer hires more labour so long as the MP of that labour exceeds the marginal cost of that labour, MCL

The wage paid equals the MP of the labour hired

In a competitive labour market, a minimum wage creates a kinked supply curve

In a competitive labour market where a minimum wage has already increased the wage, a rise in the minimum wage always reduces the quantity of labour that is demanded

In a monopsonistic labour market, a minimum wage creates a two-part MCL curve

In a monopsonistic labour market where a minimum wage has alreadt increased the wage, a rise in the minimum wage always reduces the quantity of labour that is demanded

They have many roles in addition to negotiating wages

If they negotiate a higher wage in a competitive labour market, they will result in employers wanting to hire less labour

If they negotiate a higher wage with a monopsonistic employer, they will always make the employer want less labour

They may attempt to alter the demand curve for labour

Efficiency wages are paid only to discourage shirking

Efficiency wages discourage shirking because they create an excess supply of labour, so a shirking worker who was dismissed might face a lengthy period of unemployment

The no shirking constraint curve shows the number of non-shirkers who could be hired at each wage

The efficiency wage is above the market wage

It is always illegal for employers in the UK to discriminate on race or gender

Employers are most likely to discriminate against applicants from particular groups if the wage is held above the market wage, for example because of a minimum wage law.

It is irrational for a profit-maximizing firm to pay different wages to different genders for the same work, unless they or their clients believe one gender performs better than the other

Females earn less on average than males, partly because within each occupation, males hold a disproportionate share of the better paid jobs, and partly because women tend more often to work in low paid occupations