Party leader Leanne Wood has said Plaid Cymru would vote against a Labour budget if it included cuts that would affect the poor.
Speaking on the Today programme on Radio 4, Leanne Wood said: “We would be prepared to vote down a Budget by Labour if it was pushing, putting forward, more cuts on the backs of the poor.
“We’ve said throughout this campaign that austerity has hurt those with the least, and that has to stop.”
Leanne Wood urged Ed Miliband to work with Plaid Cymru to keep the Conservatives out of government.
Her statement echoes similar comments made by the Green Party and SNP.
However, Labour leader Ed Miliband has ruled out any formal deal with Plaid Cymru.
Plaid is unlikely to win more than a handful of MPs in Thursday’s general election, but smaller parties could play an important role in the event of a minority Labour government.
New research warns that the number of food bank users could double to two million if the Conservatives win the election on Thursday.
Commenting on the findings, Labour’s Shadow Work and Pensions Secretary Rachel Reeves said: “It would be an absolute disgrace for food bank use to double.
“The welfare state is there to provide a safety net. It’s not doing what it’s meant to do when people have to rely on charity.”
Reeves said Tory plans for a further £12bn in welfare cuts could not be achieved without hitting tax credits and child benefit.
She said: “Labour will protect them, and families across the country now know the Tories will cut them again”.