Labour heavyweight Peter Hain has torn into the party's flagship announcement on cutting winter fuel benefits for rich pensioners, saying it will raise "peanuts".
The former cabinet minister, who has been a loyal supporter of Ed Miliband's leadership, said the "attack on pensioners' allowances" could signal a "slippery slope" towards providing US-style public services only for poor people.
"First the money raised is estimated at 100 million which is peanuts in terms of the wider welfare budget let alone total government spending," he wrote.
"Second it begs the question; if winter fuel allowances are to be means tested then how far does the means testing go, does it stop at fuel or will TV licences, bus passes and senior rail cards come next?
"Third, if middle Britain ceased to benefit from the welfare state through some of the few universal benefits that are left, how can we convince them to fund the larger part of that budget through their taxes?"
He raised fears this was "the top of a slippery slope towards US-type system of public services for the poor only".
"The attack on pensioners' allowances leaves a big question hovering over the future of the welfare state: is it for everyone, or just for the poor?"
The welfare system is founded on universality, he said, "in the laudable hope of cementing social solidarity."
A similar point was made by Miliband himself recently.
Hain said: "Announcements such as today's alter that original aim dismantling the very universalism upon which that solidarity relies."
The winter fuel allowance is "a symbol of social cohesion and respect for senior citizenship," he wrote, and warned that "the social and political cost" of taking them away could be "huge".
"What would this say about a society of soaring bankers' bonuses?"
In April, Hain said that trying to justify the move on cost grounds - being touted at the time by the Lib Dems - would be "mendacious".
In his blog, the former Welsh Secretary, who backed Ed Miliband's campaign for Labour leader, added that he thought the rest of Balls' speech on Monday was "brilliant".