Friedrich Hayek is one of the best-known advocates of an unfettered free market. Economically speaking, he was a libertarian. This means that he was against almost all forms of government intervention in an economy. Hayek believed that government planning in an economy was a inherently dangerous because that was the path that led to totalitarianism.
To Hayek, "liberty" or "freedom" refers to the freedom from arbitrary government dictates. He argues (in the hayek.htm link below) that these words mean
...freedom from coercion, from the arbitrary power of other men.
The key word here is "arbitrary." Hayek believes that the government must not act in arbitrary ways. As he says in the eNotes link below
... government in all its actions is bound by rules fixed and announced beforehand—rules which make it possible to foresee with fair certainty how the authority will use its coercive powers in given circumstances and to plan one's individual affairs on the basis of this knowledge.
This, to Hayek, is liberty. It is freedom from government actions that cannot clearly be foreseen based on the laws that exist. Hayek believed that government interference in the economy was essentially arbitrary. He believed that it inevitably led to a situation in which government would use its powers in more and more unpredictable ways.