There is criticism of bonus payments offered to landowners who sign up quickly to allow a controversial gas pipeline across their properties.
The pipeline would cut through 16 miles of the beacons' park
The National Grid has offered the money to landowners in Brecon who agree within six weeks that the gas supply could cross their land.
One landowner, offered £1,000 more if he signs up soon, said farmers were feeling "pressured" into signing up.
National Grid said the compensation offer was a nationally agreed formula.
The utility firm wants the 115-mile pipeline to carry natural gas from two liquefied natural gas (LNG) terminals currently under construction at Milford Haven.
LNG will come into the port in tankers and be re-gasified at the terminals before entering the pipeline network.
The proposed pipeline carrying the gas will run from Felindre, near Swansea, to Tirley, between Newent and Tewkesbury in Gloucestershire, cutting through 16 miles of the Brecon Beacons National Park and the Wye Valley.
The proposal is still some way off being approved or rejected by the Department of Trade and Industry (DTI), and the Brecon Beacons National Park Authority is among opponents, saying the pipeline could damage the local economy and environment.
Meanwhile the National Grid is hosting a series of meetings with landowners, farmers and tenant farmers in the area who could be affected.
National Grid is holding meetings about the beacons' route
A final consultation meeting is on 18 January, and landowners who agree to the compensation offer within six weeks of that will earn an additional payment.
Landowner Gavin Hogg, who runs the Green Man Mountain Boarding Centre near Brecon, was offered £1,000 more if he signs within six weeks.
But he told the BBC News website the offer made it appear the plan was a "done deal".
He said: "You have to read well into the document to get to a small paragraph saying that it's subject to consent. The documentation that appears on your desk makes it seem a fait accompli."
"It just seems to me that a whole lot of questions needed to be answered before the company reached this stage."
A spokeswoman for National Grid said the bonus offer was part of UK-wide scheme which had been in place for 35 years.
She said: "It's extremely important to talk in the very early stages to the landowners and tenants whose land we will be crossing.
"The last thing we want is for the landowners and tenants to lose out. We would urge them all to employ a land agent."
National Grid must complete a year-long environmental impact study this summer before it can approach the DTI about the proposed pipeline, which it says would be buried 1.2 metres underground.
Once complete, the pipeline will transport around 20% of gas needed to meet UK consumption.
The Brecon Beacons National Park Authority, which opposes the scheme, has also been made a compensation offer which authority members will consider next week.
A spokeswoman said: "We can confirm that we have received a contract to purchase land for the proposed gas pipeline that runs through the national park, and we are still in discussions with National Grid."