An election row has flared after Labour revealed it has given another £2m to the Children's Hospital for Wales.
Catherine Zeta Jones opened the first phase of the £21m project
Brian Gibbons said the decision was taken at the end of March, as one of his last acts as health minister before Thursday's assembly poll was called.
He said he had kept it secret to avoid charges of making political capital.
The Liberal Democrats have complained to Wales' top civil servant, Plaid said it was "blatant electioneering" and the Conservatives called it "cynical".
The Lib Dems complained to Wales' top civil servant, asking whether Dr Gibbons had breached ministerial regulations by revealing the extra funding during the campaign.
Assembly permanent secretary Sir Jon Shortridge has told the Lib Dems it is not a matter for him, and that Welsh Labour leader Rhodri Morgan is responsible for policing the regulations.
Mr German will now write to Morgan asking for a statement on whether he believes Dr Gibbons' letter has breached the code.
The controversy began after the Western Mail printed a letter from Dr Gibbons in response to the newspaper's criticism of the hospital's £5m funding gap.
Dr Gibbons told the Western Mail that an extra £2m assembly government backing would "substantially reduce" that gap.
The first phase of the £21m specialist unit for sick children was opened last year by Welsh Hollywood star Catherine Zeta Jones, patron of the public fundraising appeal.
The second phase - once built - will house an intensive care unit, operating theatres and surgical wards, at the University Hospital of Wales in Cardiff.
The hospital at the University Hospital of Wales in Cardiff
Dr Gibbons wrote in Tuesday's Western Mail: "At the end of March I decided not to make this decision public, precisely because I was convinced that, to do so just on the cusp of the election campaign, would lead to the sort of charges of claiming political advantage in which... this project ought not to become embroiled."
But Plaid Cymru criticised the timing of Dr Gibbons' announcement, 48 hours before polling.
Helen Mary Jones, the party's health spokesperson, said: "While we are glad the money has become available, this seems a case of blatant electioneering.
"If the money was there a few months ago we should have been told.
Conservative assembly group leader Nick Bourne said: "While we welcome any extra money for the children's hospital I am extremely concerned that Brian Gibbons has chosen to make this announcement just 48 hours before polling day.
"There will be many people in Wales who will see it as a cynical election ploy.
"Brian Gibbons says this decision was taken in March but the announcement delayed to avoid him being accused of using it for political advantage. Yet today we have him doing just that."
Jenny Randerson, for the Lib Dems, said: "This is unbelievable that a minister has chosen to break the rules that clearly define how they should act in a pre-election period.
"This desperate attempt to save Labour from meltdown seems to be a clear breach of the ministerial code.
"The Welsh Liberal Democrats are committed to giving the full amount to complete the hospital in the shortest possible time."
A Labour spokesperson said in response: "Brian Gibbons' letter makes it clear that he felt it necessary to rebut criticism in various newspaper articles that the Government was somehow 'dragging its feet' over the issue of phase two of the children's hospital.
"His letter makes clear that he had not intended to make any statement about the extra funding during the election campaign - but felt given the criticism that he needed to set the record straight.
"Welsh Labour is fully committed to seeing phase two of the children's hospital up and running, and no-one will be happier than us to see the project moving forward.