Key word "Discuss' Two sided discussion.

Potential disadvantages: 

• there might be industrial action 
• powerful unions/industrial action could lead to disruption of the economy 
• this could lead to a firm going out of business, causing an increase in unemployment 
• this could affect output and damage reputation of country 
• powerful trade unions could lead to higher wages 
• making products uncompetitive in world markets. 

Potential advantages:

• can work with employers, not always against them 
• can work with government, e.g. to support legislation. 

Demand and supply diagram based on restricting supply

Answer must include:

axes correctly labelled (wage/price and employment/quantity) (1) 

demand and supply curves correctly labelled (1) 

shift of supply curve to the left (1) 

rise in wage/price and fall in employment/quantity (1)