Senator Gary Humphries.

Senator Gary Humphries. Photo: Andrew Meares

Significant support is emerging from the Coalition frontbench, including the leadership team, for the embattled ACT Liberal Gary Humphries in his preselection challenge with Zed Seselja.

Many of Senator Humphries' frontbench colleagues expressed their support for him on Thursday, following the strong intervention of Tony Abbott.

The Opposition Leader hit out at ''ambushes'' in preselection contests and praised Senator Humphries' political skills.

Mr Abbott was speaking at a function where a petition was circulated calling for the preselection process to be overturned on the basis that many of Senator Humphries' supporters have been disenfranchised.

Eligible Liberal Party members will vote on February 23 to choose the candidate to stand for the party for the ACT Senate spot.

Senator Humphries has previously received support from senior Liberal frontbench members Joe Hockey and Eric Abetz, along with Nationals Senate leader Barnaby Joyce.

Deputy Opposition Leader Julie Bishop said she wanted to see Senator Humphries as part of the Coalition team fighting the September election.

The Coalition's parliamentary tactician, fellow moderate

Christopher Pyne, has written to ACT Liberal Party members extolling Senator Humphries' experience.

''If the federal Coalition is fortunate to be elected in September, Canberrans will need Gary's experience to deliver for them in what will be tight fiscal and economic circumstances for an incoming Coalition government,'' he says.

''Gary is an indefatigable campaigner … [and] has fought off real challenges from the Greens by combining a hard-nosed approach to economics with compassion and caring for people and Canberra's unique circumstance as the nation's capital.

''To be sure of winning one of the two seats in the Senate in the ACT, now is not the time to be 'changing horses midstream'.'' Shadow attorney-general George Brandis said it was unconscionable to consider losing ''such a tremendous asset'' as Senator Humphries.

''I've got skin in this game - Gary is my parliamentary secretary and I don't want to lose him,'' Senator Brandis said.

''It seriously annoys me that he is under threat.

''I couldn't but endorse what Tony Abbott says, that preselection contests are fine, they are part of our democratic tradition, but they've got to be fair, open, transparent and not ambushes.''

Senator Brandis described his parliamentary secretary as a perfect colleague. ''He's been hardworking, he's been loyal, he's been across everything, he's been diligent, he's been a good colleague and beneath his famously polite persona he's been a formidable enemy of the Labor Party,'' he said.

''That is evidenced by the fact that in this shockingly left-wing city he actually won an election and served as chief minister.

''He is and I hope will continue to be, a glorious asset to our team.''

On Thursday, veterans affairs spokesman Michael Ronaldson described Senator Humphries as a ''strong fighter for Canberra''.

Environment spokesman Greg Hunt said: ''I have great respect for both candidates but always support my sitting colleagues and note that Garry has been a tremendous partner in local environmental initiatives such as Green Army.''

Justice spokesman Michael Keenan said he attended the event on Wednesday because he appreciated Senator Humphries' intelligence and ability.

''I also have seen firsthand that he will put the interests of Canberra first and I respect that quality in local members,'' he said.

Defence science spokesman Stuart Robert said: ''Gary is a hard-working member of the Coalition's shadow defence team and has always enjoyed my support.''