Why is the Petrov Affair considered an important event in Australia's repsonse to the threat of communism?

The Petrov Affair, which happened in 1954, was important
because it led to the breaking of diplomatic relations between the Soviet Union and
Australia and because it moved Australia much more firmly towards
anti-communism.

Before the Petrov Affair, there was
controversy within Australia as to how to respond to communism.  Robert Menzies, then
the Prime Minister, had tried to outlaw the Communist Party but had been overruled by
the High Court and had lost in a referendum on the issue.  This vote was extremely
close, showing that there was a great deal of public sentiment on each side of the
issue.

When the Petrov Affair happened, the dynamic changed
and Australia became much more anti-communist for some years to come.  This is seen most
clearly in the fact that diplomatic relations between the two countries were severed and
were not restored at all for five years.