The NFUS and the Scottish Rural Property and Business Association (SRPBA), have submitted to the public inquiry about a proposed 135-mile electricity transmission line between Inverness and Stirling.
The inquiry began in early February and is expected to be complete later this year. It is focusing on an application from Scottish & Southern Energy and ScottishPower to construct a 400,000 volt line with about 600 pylons, most of which will be more than 160ft high.
Both NFUS and the SRPBA say they see the need for additional transmission capabilities to support renewable energy projects in the Highlands, but feel that the feasibility of putting the cables underground has not be given enough consideration.
Nigel Miller, vice-president of NFUS, said: "Before we erect 600 pylons, each around the height of the Scott Monument in Edinburgh, every single alternative must be looked at. Unless we can see evidence that overhead lines are the only viable option, we cannot support them. To date, we have seen no such evidence.
"This will be one of the largest industrial developments the Highlands has ever seen, so time needs to be taken to ensure a proper analysis of the options is completed. Our members in areas the line is proposed to go through deserve nothing less. We know that underground cabling is more costly, but this cost needs to be weighed against the potential blight in terms of planning and tourism that pylons could bring with them."