The federal Environment Department decided UPC Robbins Island's 115 kilometre transmission line between Robbins Island Rd at West Montagu and Hampshire was a controlled action under the Environment Protection and Biodiversity Conservation Act and would require assessment and approval under the act before it could proceed.

The department said that was because of listed threatened species and communities.

The projects are opposed by environmentalists, including the Bob Brown Foundation.

Foundation campaigner Scott Jordan describes the transmission project as a biodiversity catastrophe and the big wind farm proposed for Robbins Island as a migratory bird armageddon.

"The biggest problem in the Minister's decision is they're assessing each stage of this project separately," Mr Jordan said on Friday.

"There are two wind farms that can't proceed without the transmission line and the transmission line won't proceed without the two wind farms."

Mr Jordan said the act required projects not to be referred as "piecemeal applications", but that was what was happening.

He argued separate assessments would avoid assessment of the full impact the combined projects would have on threatened species and the environment.

A UPC spokesman said it submitted separate applications following advice and guidance from state and federal regulators.

"As part of this process, the project specific guidelines include the need to assess cumulative impacts of the project," he said.

"UPC continue to work with the regulators to ensure a rigorous environmental assessment is done for all three projects."

Tasmanian Energy Minister Guy Barnett recently said the government required wind farm proponents and operators to minimise effects on threatened species and transmission lines were subject to rigorous planning and legislative procedures.