Outspoken Campbelltown councillor Russell Matheson confirmed last week that he gave up his independent status about six weeks ago to join the Liberal Party.

The move has shocked the Macarthur community, because Cr Matheson has always been more closely associated with the Labor Party.

The NSW division of the Liberal Party confirmed the two candidates for preselection and said a decision would be made in the next few weeks, but said no date had been set.

Cr Matheson confirmed yesterday that the Liberal Party had approached him to nominate as a candidate.

``I've been on Campbelltown Council for 17 years, lived in Campbelltown for 30 years, and I think I've got a good connection to the broader Macarthur area,'' he said.

Cr Matheson said a battle with the NSW Planning Department over the gas-fired power plant at Leafs Gully had been a catalyst for him to nominate for preselection, even though that issue was a state one.

He said he hoped people would recognise his name previously listed as an independent on ballot papers and vote for him.

``I've got the ability to be a strong advocate,'' he said.

Cr Matheson said Mr Farmer had done a good job for the area, and that the decision would come down to local branch members.

Mr Farmer left on Monday for a mission trip to a Thailand orphanage for children with HIV/AIDS, and his office was unsure as to whether he knew who his challenger was.

In a statement before he left, Mr Farmer said he would strongly contest the preselection process and said he wanted to continue as Macarthur MP.

``Sitting members should be open to challenge and I don't back away from that view,'' he said. ``It is important that we provide the opportunity for people to seek nomination for a seat so that we can encourage new talent into the parliament.''

The Australian Electoral Commission is in the process of determining new seat boundaries.