Campaigners will try to stop the National Grid forcibly buying land for a natural gas pipeline that will span the breadth of Wales.
The first phase of construction is well under way
Opponents of the pipe linking liquefied natural gas (LNG) plants in west Wales with Gloucestershire have set up a group called Safe Haven Network.
The group will lobby landowners along the route of the proposed pipeline.
The National Grid said compulsory purchasing was sometimes necessary when constructing very important projects.
The campaign group, which met in Carmarthen on Saturday, is an offshoot of Safe Haven - which failed in its attempts to stop the construction of two LNG terminals in Pembrokeshire.
But the network said it would consider legal action to stop the plans.
Member Linda Ware, from the Cilfrew Residents' Association, said the group wished to speak to the Welsh Assembly Government and National Grid.
She added: "Have we got no rights? What we want is democracy and to be able to get the answers that we want."
Adam Price, Plaid Cymru MP for Carmarthen East and Dinefwr, said there appeared to be an "unseemly haste" by the UK government and the company to get the project through.
He told BBC Wales: "That's driven not by Wales' needs, it's driven by the energy needs as they're perceived here down in London.
"It's London unfortunately trumping legitimate concerns in Wales once again."
Construction of the first phase of the pipe from Milford Haven to Aberdulais near Neath is already well under way.
When finished, the 115-mile (185km) pipe will carry 20% of the UK's gas.
But the second phase of the pipeline - through the Brecon Beacons National Park - still needs approval from the Department of Trade and Industry.
National Grid also needs land for the second phase of construction.
A spokesman for the company said the pipeline was a "a very important project for Wales and for the United Kingdom which is in the national need".
"Sometimes, unfortunately, compulsory purchase orders are needed," he said.
"The route we've achieved through the north of the national park we believe is the best overall."