A new seat in south-west Sydney called Leppington,nominally Labor,would be created.
Three of the Coalition's already marginal seats - Heathcote,Penrith and Upper Hunter- could become more at risk under the proposed changes while Kogarah could be a problem for Labor.
Mr Ayres holds Penrith with a 1.3 per cent margin,Nationals MP Michael Johnsen has a 2.5 per cent margin in Upper Hunter and Liberal MP Lee Evans is on 4.9 per cent in Heathcote.
A senior Liberal Party source said:"Penrith and Upper Hunter will be hard but still very winnable and Heathcote will be harder but is also winnable."
Mr Minns,who challenged Jodi McKay for the Labor leadership last year,has a wafer thin margin of 1.7 per cent on Kogarah after suffering a swing against him at the last election.
Several Labor sources said it is expected Labor would challenge the proposed changes to Kogarah.