The Boundary Commission of England (BCE) has said it will continue with proposals for a constituency consisting of Bude and Launceston in Cornwall, and Bideford in North Devon.
Cornwall Council said it will be continuing its campaign to protect its historic boundaries and will be lobbying Parliament as it "strongly objects to this proposal".
We strongly believe there are cultural, legal, geographic and political reasons to maintain our border in terms of Parliamentary representation and we will be lobbying Parliament and calling on the Boundary Commission to rethink this proposal. >
The Council has argued that the proposals will conflict with the spirit and intent of the recognition of Cornwall's minority status, which was granted by the European Union.
A spokesperson said it will also be "destroying the integrity of Cornwall’s historic border, which would cause great distress to numerous residents."
Last year the BCE began a national review of constituencies in a bid to equalise the size of each, and reduce the number of MPs from 650 to 600.
Cornwall Council has long opposed a merge with Devon, when proposals were first announced in 2010.
This secondary consultation period will run until 27 March 2017. A final consultation will run in late 2017/ early 2018 with revised proposals. The BCE must take its final recommendation to Parliament in September 2018.
If agreed upon by Parliament the new constituencies will be in use at the next scheduled General Election in 2020.