The Evangelical Alliance has found 23% are still undecided who they will back in the general election.
Labour is narrowly behind the Conservatives, according to the new poll, with a three point gap separating the parties.
The Liberal Democrats have slightly recovered in the last seven months to reclaim third spot on 12 per cent, and the Green Party has increased its support to nine per cent. Support for UKIP has dropped from 12 to 10 per cent over the same period.
The EA says around half a million voters are still unsure which way they will vote.
Half of these voters are considering voting for Labour, slightly fewer for the Liberal Democrats and 44 per cent for the Conservatives. Among the minor parties the Greens are an option for 26 per cent while only 16 per cent are thinking about voting for UKIP.
Dr Dave Landrum, director of advocacy at the Evangelical Alliance, said: "With only days left before the country goes to the polls many evangelicals are still on the fence.
"Given that our research shows they intend to vote in great numbers, this poll signals an opportunity for the parties.
"Let's hope they take this opportunity by addressing the concerns of evangelicals in the final days of campaigning, including poverty and religious freedom."