A Tasmanian Jacqui Lambie Network (JLN) MP says the position of the state's infrastructure minister is "untenable" over his handling of the roll-out of two new Spirit of Tasmania vessels.
JLN Lyons MP Andrew Jenner made the comments on Monday afternoon, just days after Senator Jacqui Lambie demanded the resignation of Michael Ferguson.
The JLN is in a formal agreement with the Liberal government over supply and confidence.
But the government has been under increasing pressure over the Spirit of Tasmania roll-out, culminating in a public stoush last week with the chair of government-owned Spirit operator, TT-Line.
Michael Ferguson (right) is Infrastructure Minister and Deputy Premier in Jeremy Rockliff's (left) minority Liberal government. (ABC News: Maren Preuss)
It centred on delays and cost blowouts to port infrastructure at Devonport which would see the new Spirit vessels initially operating at reduced capacity, having already seen cost escalations with their Finnish shipbuilder.
Mr Jenner said he had become increasingly concerned with the matter.
"We've got the largest infrastructure build ever going on, and it's now not only taken years over, but it's blown the budget," he said.
"The buck has to stop somewhere, and I guess it stops at the top.
"So that's my own opinion. That it is untenable, but that's for [Mr Ferguson] to come and agree to."
Mr Ferguson is the deputy premier and treasurer, and is one of the most senior members of Premier Jeremy Rockliff's cabinet.
TT-Line operates independently of government, but Mr Ferguson has been its shareholder minister, including throughout the period of escalating delays.
Cost blowouts and delays were not publicly known until Labor started questioning the matter in parliament.
The JLN agreed to support the government in confidence and censure votes, except in cases of malfeasance or corruption.
Precarious grip on power
Mr Jenner stopped short of saying he would support a no confidence motion in Mr Ferguson, instead wanting to hear evidence from former TT-Line chair, Michael Grainger.
The government asked Mr Grainger to resign as chair last week, claiming he had "engaged in the blame game" by issuing a media release on Wednesday afternoon, after Mr Rockliff attempted to end the finger pointing.
Mr Grainger could give evidence to a parliamentary committee next month.
Mr Jenner said he wanted to hear both sides of the issue.
"You have to remember, Mr Grainger wanted to come forward and was sacked just days before," he said.
A no confidence motion in Mr Ferguson would require 18 votes in the House of Assembly, at which point typical parliamentary convention would be for him to resign his portfolio.
Labor has 10 votes, the Greens have five and have been long-term critics of Mr Ferguson, while the final three votes could come from a combination of Mr Jenner and independents Craig Garland, David O'Byrne or Kristie Johnston, who have also been critical of Mr Ferguson.
JLN Braddon MP Miriam Beswick said she would not support a no confidence motion, but said it was "very disappointing" that the Devonport port works had been delayed.
The planned berth for the new Spirit ferries has also been delayed, adding to the government's headaches. (Supplied: TasPorts)
Ferguson 'disappointed' by Lambie call
Just hours before Mr Jenner's comments, Mr Ferguson was asked about Ms Lambie's calls for his resignation.
"That was disappointing, because we're all working so effectively and properly together in Tasmania," Mr Ferguson said.
"The JLN members have been first class politicians to work with.
"They've been honest. They've provided stability in a circumstance where no major party had a majority of members in the House, and they're actually just good people."
Mr Ferguson declined to comment on Mr Jenner's remarks.
Lambie backs call for Ferguson to be demoted
In a press release on Monday night, Ms Lambie said suggestions a JLN state member "calling for Mr Ferguson to resign breaks the … agreement with the Rockliff government, but that's rubbish".
"If the premier does the right thing and sends Mr Ferguson to the backbench so a competent minister can take the reins, then the agreement stands," Ms Lambie said.
"I congratulate Andrew Jenner for calling out Mr Ferguson and I agree with him that Mr Ferguson's position is untenable. I hope the premier sees sense and puts someone in charge that can do the job."