The charity says moving the helicopter to join one in the north will mean the service will be able to fly longer hours, doing shifts.
But many fear it will leave Powys with poorer coverage than it has now, something denied by the charity which says it will have better service.
The leaders of Powys County Council say the idea is "extremely concerning".
“The Wales Air Ambulance Service is a vital service, especially for a rural county such as Powys. It also receives a huge amount of public support from our residents,” said leader Councillor James Gibson-Watt and Deputy Leader Matthew Dorrance.
“It is therefore disappointing and extremely concerning that their proposal could see their Welshpool base close.
“We will be seeking assurances from senior representatives at Wales Air Ambulance that changes won’t impact on our residents.
"We will also be asking for an explanation for the justification for this proposal, in particular how moving their base from Welshpool to north Wales will enhance the service for our residents.”
Plaid Cymru has send a list of questions to the charity including asking whether the idea is to move the North Wales base from Caernarfon to Rhuddlan, close to the A55, and flying time from north Wales to the places like Llanidloes.
The party has also asked whether the charity has looked at extending hours at Welshpool.
The Wales Air Ambulance says that the move from Welshpool so two helicopters could work from the same base would mean flying hours would be extended with one crew working 8am until 8pm and the other 2pm until 2am.
Therefore patients in Powys and North Wales with life or limb-threatening illness or injuries after 8pm will have a local response rather than needing the busy Cardiff-based overnight crew, the service says.
"Currently, there are still people across Wales that the service is unable to attend, due to several factors. At the same time, it has valuable transport assets - helicopters and rapid response vehicles - and highly skilled clinicians who are underused," Steven Stokes from the charity said.
"Wales Air Ambulance could attend up to 26 more missions in Powys every year and increase its responses in Powys by 11per cent. This is the highest improvement increase per 1000 population of any county in Wales. It could also meet 85 per cent of the demand for its service in Powys. Currently we are meeting 79 per cent."