The parish councils of Marlesford, Little Glemham and Farnham with Stratford St Andrew have formed the Four Villages Bypass Working Group.
They fear developments at Sizewell and Greater Gabbard would see more heavy vehicles on roads which they say already struggle with traffic.
The group has appealed to senior councillors and local MPs to intervene.
EDF Energy is planning to build another nuclear power station at Sizewell by 2025.
Debbi Tayler, clerk for Farnham with Stratford St Andrew Parish Council, said: "We feel that with the push for the development of the new reactor at Sizewell, it's the best opportunity we've had in a long time, given it may be possible for us to find funding via EDF.
"Whether or not there is going to be a significant increase in traffic because of the new build will depend on the road traffic assessment that Sizewell and EDF are carrying out at the moment."
Ms Tayler said she had seen "huge propellers" passing through the villages recently en route to the Greater Gabbard offshore wind farm.
She said: "If this continues there's no way that the road can maintain that sort of traffic.
"It's crazy that you get to Marlesford and you're on a major trunk road and it's a single carriageway that goes through very, very small villages."
Therese Coffey, Conservative MP for Suffolk Coastal, said: "Everyone who drives up and down the A12 will understand the problem that the residents of the four villages experience.
"We are determined to work together to get the best solution for residents and businesses alike."
A spokesman for Suffolk County Council said it supported the aim of a "four village bypass".
"We believe that this should be delivered as part of the proposed Sizewell C development," the authority said.
Four villages have grouped together to campaign for a new A12 bypass in Suffolk.