Activists for the Coalition for Marriage (C4M) group urged people in Truro, Camborne and Liskeard to lobby their MPs against plans to allow gay marriage in places of worship.
The proposals, introduced by the Conservative/ Liberal Democrat coalition, would mark a major change from civil partnerships, which have been able to take place since 2005.
C4M’s national campaign director, Colin Hart, said: “Our local activists are fired up to make sure voters have their say. We have identified these three marginal Cornish seats as key, together with 62 others nationwide. MPs can expect local voters to be pressing them on where they stand on the redefinition of marriage.
“These plans are unpopular and divisive. The voters were ignored by the politicians, this was in no party’s manifesto and the public consultation was a sham. The Government should concentrate on reviving the economy and delivering better public services, that’s what ordinary people want – not playing politics with marriage.”
Sarah Newton, MP for Truro and Falmouth, has said she personally supports proposals to allow gay marriage – but will let her constituents influence how she votes on the issue.