As Collingwood prepares to play Hawthorn in the preliminary final tonight not everyone is getting into the finals spirit.

One of Australia's biggest property developers, Mirvac, is threatening a Mulgrave couple with legal action if they do not lower the Collingwood flag flying from their house near Waverley Park.

The flag is flying across the road from the entry to the Hawthorn Football Club.

David Austin, 55, said the flag has been proudly fluttering above his two-storey house for more than two months. The flag flies from a professionally installed flagpole on the roof.