Right to information (RTI) documents obtained by Labor show the state government and TasRail thought the money promised by the Morrison Government for a new minerals shiploader at the Burnie port in the lead-up to last May's election would be new funding.

The documents show they learned in October - after the election - the money would come out of funds for the $136 million third tranche of rail network improvements in Tasmania.

Labor fears the shortfall will lead to rail network deterioration and possibly even derailments.

One of the documents, from TasRail, said the rail network would deteriorate, leading to reduced service levels and derailments, in the absence of a capital renewal program.

Shadow Infrastructure Minister Shane Broad said the shiploader and rail improvements were both needed and Labor supported both.

He said the federal government had not been honest about whether the $40 million would be new money.

"Now we know, and it's quite clear from the RTI, that TasRail thought it was new money, the state government thought it was new money," Dr Broad said.

"The federal government after the election decided to use existing money, dudding TasRail.

"It's only been revealed through RTI."

Dr Broad asked Infrastructure Minister Michael Ferguson during government business enterprise hearings in December if he was surprised to hear the shiploader funding would come from the rail revitalisation program, rather than being additional funding.

Mr Ferguson's answers did not reveal if he was surprised or not.

"He knew the answer and wouldn't admit that they had been dudded by the federal government," Dr Broad said.

"Why can't they put that argument up (to make it new money)?

"Why are they just rolling over and not doing anything about it?"

On Thursday, Mr Ferguson said funding the shiploader project through tranche three guaranteed the funding, and it was brought forward by the Morrison Government late last year.

"This means the shiploader, which is a critical project for our state's mineral export sector and is strongly endorsed by industry stakeholders, will happen sooner," Mr Ferguson said.

"It's disgusting that Labor continues to oppose the replacement of the critical Burnie port shiploader at a state or federal level even though it is funded and going ahead.

"TasRail is currently working to deliver projects under tranche two.

"There is no reduction or compromise on other projects under tranche three, which are currently under consideration.

"Once project plans are settled, further state and federal funding can be considered to further expand the program, if required.

"I'm advised the inclusion of the $40 million commitment to tranche three of the Tasmanian Freight Rail Revitalisation Program not only guarantees its funding, but will bring forward the construction to later this year.

"Furthermore, the federal government has indicated that if more funds are required, this will be considered."

Braddon Liberal MHR Gavin Pearce said the upgrade of the ageing shiploader was important to the region and he welcomed "the federal government's recent commitment to bring forward funding to allow the project to begin immediately".

"To ensure that planning works could progress immediately, the federal government prioritised this funding from the commitment to tranche three of the Tasmanian Freight Rail Revitalisation Program."

Mr Pearce said specific projects to be funded under tranche three were still being considered by TasRail and the Tasmanian government.

"Once a program of work has been established and costs determined, additional funding can be considered in future federal budgets to extend tranche three works if required," he said.

"I work every day to ensure that Braddon receives the funding required to progress all major projects that are vital for of our region."