An online petition demanding the second severn bridge is not named after Prince Charles has attracted 25,000 signatures.
Scores of people also took to the streets calling for the M4 motorway bridge that connects England and Wales to be named after "someone who has achieved something for our nation".
Protesters at one demonstration in Cardiff held Welsh flags and homemade signs with slogans that included: "No to the Prince of Wales bridge! Let the people decide".
Another called the move: "Pointless expensive propaganda".