Changes aimed at giving paramedics a much-needed rest could end up doing the opposite, Tasmanian authorities say.

Ambulance Tasmania is looking at a change to two 12-hour day shifts and two 12-hour night shifts.

Currently, paramedics are on four-day blocks of two 10-hour day shifts and two 14-hour night shifts.

Health and Community Services Union's Tim Jacobson says the change will not help.

“On a 14-hour shift staff get two meal breaks, so there’s the capacity for those staff to rest and recuperate,” he told the ABC.

“But in the 12-hour roster that's been proposed, Ambulance Tasmania has only provided for one meal break, so in our view it will actually result in increased fatigue, not reduced fatigue.”

He said many did not see the purpose of the change.

“There's absolutely no doubt that the 10-14 hour shift, while it does have very lengthy shift times, is very popular amongst paramedics.

“The fundamental issue that we've had historically with fatigue on those shifts is where those shifts have been extended.”

Dominic Morgan from Ambulance Tasmania told reporters that he only wanted what was best for staff.

“I struggle to understand how reducing someone's potential possibility of working a 16-hour shift would be actually made worse by only requiring them to work 12,” the chief executive said.

“The most important thing to point out here is that it's not the union that has the work, health and safety responsibility, my job is to ensure that our workforce goes home safely.

“My view is that not doing 14-hour night shifts improves workplace health and safety.

“The advice I've received so far is that the workforce are generally more supportive of the 12-hour shift, because it preserves a four days on, four days off roster.”