Hayek's defense of competition regulation This article claims Hayek endorsed competition regulation:


  As it evolved, neoliberalism became more strident. Hayek’s view that governments should regulate competition to prevent monopolies from forming gave way – among American apostles such as Milton Friedman – to the belief that monopoly power could be seen as a reward for efficiency.


In which work did Hayek advance such view?
This article states:


  In  both  of  his  seminal  works  in  political  theory, 
  The  Constitution  of  Liberty  and Law, Legislation and Liberty, Hayek endorsed as a legitimate function of the state the  power  to  regulate  monopolies  and  curtail  industry  practices  in  restraint  of  trade. 


For example, in the first book, in Chapter 15, Hayek declares the importance of the nature of government intervention:



Notice that Hayek considered trade unions as workers' monopolistic institutions that damaged free market. Hence, in his view, these are undesirable. In Chapter 18 of the above books it says:



More on monopoly is in Chapter 17: