Reedy Marsh man Andrew Ricketts - who has sent and received correspondence with the minister over the prison issue - claims that the overarching Protection of Agricultural Land Policy results in a requirement that the prison not be build within 200 metres of the farms next door, with specifics in the Tasmanian Planning Scheme.

This would push the prison further into the informal reserve and closer to a wedge-tailed eagles nest, among other logistical problems such as more vegetation clearing and the potential for more excavation into dolerite rock.

Two properties immediately adjoining the proposed prison location - a Forico plantation and a grazing operation - are zoned Rural Resource. Under the Tasmanian Planning Scheme, such properties are afforded a 200-metre setback from their boundaries if a development of "sensitive use" is proposed.

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Sensitive use, as the planning scheme details, includes buildings that result in "the presence of people for extended periods except in the course of their employment".

Mr Ricketts said a prison would fall under this definition, meaning the setback would apply.

He said the protections were guaranteed in the Protection of Agricultural Land Policy, one of three such policies in Tasmania that provide overarching powers on planning decisions.

"And it becomes even more of a problem if they're thinking of knocking down vegetation, it makes it very hard to argue that the 200-metre setback should be relaxed," Mr Ricketts said.

"It's serious, because it's underpinned with the state policy which carries more weight than codes, such as the bushfire code or the heritage code.

"It's extremely difficult to get rid of a state policy, such as the Protection of Agricultural Land Policy."

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The Protection of Agricultural Land Policy, and associated setback, is designed to avoid non-agricultural development - such as a prison - impacting agricultural activity on farms, regardless of the zoning for the prison land. The setback applies for structures such as schools, hospitals, childcare centres, dwellings, caravan parks and any use that requires people to be gathered for "extended periods".

Mr Ricketts said he was not anti-prison, but believed the government had created even more problems by choosing the Brushy Rivulet land after abandoning its original intention to build the prison at the industrial estate on Westbury's northern fringe.

"It either needs to be near Launceston or Devonport, but Devonport is difficult because it has so much prime agricultural land nearby," he said.

"I'm sure the government would be able to find a bit of land that's not going to affect nearby agriculture, that's not going to be right in the face of a small community and that's not going to be bushfire prone."

The agricultural land setback might not be the only setback that could cause headaches for the government.

The prison requires a 100-metre bushfire buffer zone around its perimeter, which initially turned the 16-hectare prison footprint into a 19.5-hectare footprint.

But members of the group Concerned Residents Opposed to the Westbury Prison Site claimed they had been informed by the Department of Justice that the plan was to incorporate the 100-metre buffer within the 16-hectare prison footprint.

When asked if the government believes the prison would qualify as a "sensitive use" under the planning scheme and if a 200-metre setback would apply, a government spokesperson said this would be determined "once a planning application is submitted for assessment and will depend on how the land is zoned" for the prison.

"Work is ongoing to support master planning and site development options," the spokesperson said.

The government also could not confirm if the bushfire buffer would be incorporated into the 16-hectare prison footprint.

"Investigations are currently being undertaken as to the requirements for bushfire hazard management and any related buffer areas," the government spokesperson said.