The York for Europe and North Yorkshire for Europe groups say Liberal Democrat supporters have promised to vote Labour in York Outer, where the Tories have a majority of 8,289 under Julian Sturdy.
Meanwhile the group claims Labour supporters have pledged to vote for the Liberal Democrats in Harrogate and Knaresborough, where sitting Conservative Andrew Jones won in 2017 with a majority of 18,186.
Campaigners met in York and Harrogate to finalise what they described as a vote-swapping alliance.
But Labour denied their supporters were backing the Liberal Democrats in Harrogate.
Mark Sewards, Labour candidate for Harrogate & Knaresborough, described the apparent alliance as a "desperate stunt for publicity".
He said: "Labour are standing strong in Harrogate and Knaresborough. In 2017, we doubled our share of the vote and secured our best result in the constituency for over 50 years.
"I’m incredibly proud to lead a team of amazing Labour members and activists here. Together, we’ve already spoken to thousands of residents and delivered tens of thousands of leaflets since the election was called.
"While the Liberal Democrats continue to pull desperate stunts for publicity, we’ll be out on the doorsteps campaigning for every single vote on Thursday.
"Labour are the only party offering a real alternative to the Conservatives in Harrogate and Knaresborough and we are the only party offering a public vote on the final Brexit deal.”
York for Europe and North Yorkshire for Europe says Boris Johnson and the Conservatives would be disastrous for the region and that party leaders fighting each other, instead of Boris Johnson, has increased the chances of a Conservative majority.
Martin Brooks, chair of York for Europe said, "This is a very simple solution to the muddle we find ourselves in: Rather than wasting energy fighting each other it makes much more sense to combine our voting power to unseat the sitting Tory MP.
"We’re at the crunch point now and it’s time to put party tribalism aside and put the country first."
According to the final YouGov MRP polling released this week, the Conservatives are on course to get 50 per cent of the vote in Harrogate and Knaresborough, with the Liberal Democrats on 38 per cent and Labour on ten per cent.
In York Outer, the Conservatives are expected to get 47 per cent, Labour 35 per cent and the Lib Dems 17 per cent. Incumbent Conservative Julian Sturdy has told The Yorkshire Post that he considers Labour's Anna Perrett to be more of a threat to him than Lib Dem Keith Aspden.
Note: This article was amended to include the statement by Labour that its supporters were not backing the Liberal Democrats in Harrogate and Knaresborough