Plaid Cymru's coalition partnership with Labour has suffered a Valentine's Day "lovers' tiff" over a new website.
Opponents claim a political "lovers' tiff" on St Valentine's Day
Plaid launched the site to help trades unionists opt out of subscriptions to Labour, saying some did not know they were "bank-rolling" the party.
Labour called it a "particularly weak stunt from a tired party machine".
The Conservatives said the Valentine's Day "lovers' tiff" showed the two parties were "in need of some serious relationship counselling".
Meanwhile, Graham Smith, secretary of the Labour affiliated unions association, Tulo, rubbished the website.
"Nobody should forget Labour's roots within the trade union movement," said Mr Smith.
"This is Plaid showing their true colours."
But Plaid Cymru AM Leanne Wood insisted the website helped union members tackle a real issue.
"Plaid has a long history of supporting trade unionism and workers' struggles in Wales. In the last decade, many of those struggles have been against the Labour government," said the AM, who chairs Plaid's trade union section, Undeb.
"Trade unions bankroll the Labour Party; over the last six years unions have contributed £60m and many members are not aware that their money is going to the Labour Party.
"Plaid is launching a website today which will simplify what can be a difficult process."
The website named "Stop subsidising Labour" lets users click a link to a dozen of the UK's most prominent trade unions, bringing up a form to opt-out of political contributions.
But the move has clearly angered some officials in Labour, especially as the two parties are coalition partners in the Welsh Assembly Government.
A Labour spokesman said: "This is a particularly weak stunt from a tired party machine.
"Trade union members around Wales will be asking themselves where Plaid Cymru MPs were when the minimum wage was voted on in Parliament. The answer is, in bed."
Conservative assembly leader Nick Bourne added: "If this is sort of Valentine's Day present Plaid Cymru is giving to Labour, the coalition partners are clearly in need of some serious relationship counselling.
"I'd hate to see what they send if they ever do fall out of love with each other. Somehow I doubt we'll have long to wait."