George Osborne will unveil his post-election budget tomorrow (8 July) but the Labour leadership contest has been caught up in a row over a blog post ahead of the chancellor's speech.
The drama broke out after Helen Goodman, the shadow media minister, wrote a piece supporting Yvette Cooper's bid to become Ed Miliband's successor.
The Bishop Auckland MP, writing for the Huffington Post UK, said she was backing Cooper because "as a working mum, she understands the pressures on modern family life".
"We need a leader who knows what challenges ordinary people face day to day, and who is committed to helping them," she added.
Goodman then set out six "major challenges" for politicians to meet, including childcare, family finances and child protection online.
The piece was criticised by Liz Kendall's supporters after Cooper's official Twitter account shared the blog.
Labour MP John Woodcock suggested the piece was attacking Kendall because she does not have any children.
Looking forward to day someone tells a man they are voting for him cos he has a kid and the other guy doesn't. Will be equally sad then too.
— John Woodcock (@JWoodcockMP) July 6, 2015
Toby Perkins, who is leading Kendall's campaign, told BBC2's Daily Politics show: "The idea that you say 'because one of the candidates is a mother they are the one that you should back' suggests a paucity of intellectual argument that the Labour Party really should have moved beyond."
But Cooper's supporters have denied that the piece is a personal attack against Kendall.
A pro-Kendall Labour MP said: "It's absurd to suggest anyone would say being a mum is a prerequisite to being Labour leader... It's clear some around the Kendall campaign are intent on creating faux divisions and rows in the hope of lifting her campaign."
Meanwhile, Osborne is set to slash £12bn (€17bn, $18.5bn) in welfare savings as part of his emergency budget. But Downing Street has insisted that child benefit will not be cut.