Speaking during a televised debate on STV last night, Scottish Labour's deputy leader Anas Sarwar MP said: "We have been clear: if we were in power tomorrow, we would abolish the bedroom tax."
Mr Miliband has yet to say whether he will propose a repeal of the under-occupancy charge, which deducts benefits from those deemed to have spare bedrooms, in Labour's manifesto for the next UK general election in 2015.
Commenting on Mr Sarwar's remarks, a UK Labour spokesman said: "We have been pretty consistent that we think the bedroom tax should be dropped and dropped now. But with so much uncertainty over the economy, we are certainly not writing our manifesto for 2015 today."
SNP MSP Linda Fabiani, a member of Holyrood's Welfare Reform Committee, said: "On Thursday night we had Labour's Scottish leader and deputy leader appearing simultaneously on different TV channels. One says they'll scrap it, the other doesn't seem to know.
"So, if Ed Miliband is actually leading Labour, he needs to give an immediate, unequivocal commitment: would Labour scrap the bedroom tax if they were to be elected in 2015? Yes or no?
"The SNP have been unequivocal. The bedroom tax would be scrapped in year one of an independent Scotland if we were elected to office."
Benefits policy is reserved to Westminster, meaning the devolved Scottish Government cannot unilaterally scrap the charge, although the SNP administration has introduced measures to "mitigate" its impact.
Labour has attacked the policy in Scotland, where Mr Sarwar is MP for Glasgow Central, calling for a national ban on evictions, £50 million of Scottish Government cash to pay tenants' rent arrears and pledging not to evict anyone struggling with the charge in Labour council areas.
Launching the campaign on Wednesday, Scottish Labour welfare spokeswoman Jackie Baillie said a UK-wide repeal is under "active consideration" by the party, citing "newspaper speculation on when the announcement would be made, rather than whether".
Prime Minister David Cameron urged Labour to make its intentions clear at Prime Minister's Questions on Wednesday.
He said: "The question is now for Labour. You have ranted and raved about the spare-room subsidy. Are you going to reverse it? Just nod. Are you going to reverse it? Yes or no? Absolutely nothing to say, and weak with it."
Scottish Welfare Minister Margaret Burgess accused Labour of "pure hypocrisy" and "political opportunism" at Holyrood yesterday.
"We are consistent on the bedroom tax. Labour have not been consistent with the bedroom tax," she said.