Senior civil servants were so concerned at Labour ministers' spending decisions they asked for written orders to show who was responsible, says their union.
Union chief Jonathan Baume told the BBC asking for "letters of direction" was regarded as a "nuclear option".
He said "a small number" were requested in 2010, in Labour's last months and showed "some unhappiness" at decisions.
Ex-ministers have previously dismissed claims of excessive spending as "spin" by the coalition government.
The Conservative-Lib Dem government has ordered a review of all spending commitments and pilot projects signed off by Labour ministers since the start of the year.
On Monday, Chief Secretary to the Treasury David Laws told BBC Two's Newsnight: "I think we're very concerned indeed that over the last few months of this government there were a lot of spending commitments that were made and some of those may not represent good value for money."
He said that in some cases the decisions "were made against accounting officer advice".
Mr Baume, general secretary of the First Division Association which represents senior civil servants, told BBC Radio 5 Live's chief political correspondent John Pienaar: "When a permanent secretary asks for their letter of direction from a minister, it is because they feel that a serious decision is being taken, which they feel is not right.
"It's not a decision that is taken very often to ask for such a letter of direction, which is why it is regarded something of a nuclear option.
"So when it happens it tends to be a big spending decision, where the civil service believes this is not the right thing to do."
The instructions - formally titled "letters of direction" - have been sent to the Treasury, and will be sent on to the cross-party Commons public accounts committee, which evaluates public spending for propriety and value for money.
Mr Baume said the letters meant there was an "audit trail" so the permanent secretaries - who are ultimately responsible for spending decisions - can explain why they were taken.
He said he did not know which departments had asked for the letters but they would become public in due course.
"The fact that these letters of direction were being issued - a small number, as David Laws said, but nonetheless the fact that a number appear to have been issued during 2010 does indicate that there was some unhappiness about spending decisions being taken."
He said the letters might be on detailed issues on only affect a particular locality but added: "The fact that a permanent secretary feels the need to ask for a letter of direction - in other words an instruction from a minister to authorise spending, indicates that there has been a serious disagreement about that particular decision."
On 8 April a list of 15 letters of direction issued in the previous five years was published by then Treasury Minister Lord Myners.
It gave details of two issued in 2010, one relating to a shake-up of local authorities in Devon, Norfolk and Suffolk ordered by John Denham, and the other to Jack Straw's decision to provide compensation to people diagnosed with pleural plaques following exposure to asbestos.
But the Department for Business confirmed that a letter of direction was issued by one of its ministers in the first three months of this year related to Blackpool leisure assets.
A £38.9m scheme was announced by former business minister Rosie Winterton in March to refurbish and redevelop Blackpool Tower and its Winter Gardens conference centre.
Prime Minister David Cameron has said his ministers have found examples of "crazy" spending, including paying out bonuses to three-quarters of all senior civil servants.
In response, former Chancellor Alistair Darling accused the new coalition government of "playing the oldest trick on the book" by blaming its predecessor for the state of the economy.
"What do you do when you are a new government? You blame your predecessors. It is straight out of Yes Minister," he said on Monday.
On Monday, it emerged that Liam Byrne, Mr Laws' predecessor, had left him a one-sentence letter, saying: "I'm afraid to tell you there's no money left."
Mr Byrne later told the BBC that this "a phrase that chief secretaries have to get used to using".