Lib Dem MPs are under pressure to pay their interns after party leader Nick Clegg promised reform.
The party said it would push its MPs to give more help to unpaid staff - but said plans to pay interns working at party HQ will "not happen this year".
All parties at Westminster use unpaid workers - but campaigners say some are treated "appallingly" by MPs.
Mr Clegg has declared war on unpaid internships across industry claiming they are unfair on the less well-off.
Work experience placements are seen as a gateway to a successful career in professions such as politics and journalism.
But the deputy prime minister says the common practice of making young people work for nothing is barring entry to those from poorer or less well-connected backgrounds and harming social mobility.
As part of a plan to boost social mobility, he announced that informal internships for young people in the civil service would be banned.
And he told BBC he wanted the practice to end at Westminster too - starting with his own party.
He told BBC News: "From today all Liberal Democrat MPs will give real support to cover costs and to conform with minimum wage legislation as much as possible".
This was taken by some to mean that all interns would receive a salary.
But the party was forced to issue a clarification on Tuesday evening, saying plans to pay interns at the party's Cowley Street headquarters the minimum wage "would not happen this year".
The party is currently "looking for funding" to underwrite the costs.
And the party said the minimum wage commitment did not apply to interns working in the Parliamentary offices of Lib Dem MPs.
A spokesman said Mr Clegg had only promised they would be paid an "appropriate" amount - but that those taken on in the longer term by MPs should be paid at least the minimum wage, in compliance with existing law.
He said some firms had exploited interns by keeping them on for extended periods on expenses only, to avoid paying them a proper salary.
The spokesman added: "We want to make sure people aren't out of pocket."
The central Liberal Democrat Party takes on 15 interns a year, with no position lasting more than three months. All are paid expenses.
A party spokesman said: "We are continuing discussions to make sure all interns are recruited in the appropriate manner and are given the appropriate expenses in future."
He added: "We are trying to make sure there's a real improvement. We have had co-operation from all our MPs, who want to bring in the culture that he [Nick Clegg] has been trying to set out."
But Ben Lyons of the student campaign group Intern Aware said Lib Dem MPs should pay salaries to interns to make their placements affordable.
He added: "I think it's appalling. Clegg spoke about it in Parliament and he's now turned back on it.
"It's only amounting to a few pounds a day in expenses, which is hardly going to help much."
Mr Lyons also said: "If you live outside London and your parents can't afford to support you, £5 a day is going to make absolutely no difference."
"Whereas we appreciate that Mr Clegg is making noises on the issue, it just seems so poorly thought out to come back only a few hours later to say 'We haven't got any money'."