Tánaiste Frances Fitzgerald warned a Cabinet colleague that the State's forensic science laboratory was at "crisis point" due to inadequate facilities and a "chronic" shortage of space.
The Justice Minister also voiced fears about the potential contamination of DNA samples.
She made the comments in a letter to Public Expenditure Minister Paschal Donohoe last September after he had initially refused to fast-track the building of a new facility planned for Backweston, Co Kildare.
Some €6m was subsequently made available in the Budget, with building work set to begin this year.
Construction had originally been earmarked for 2019 and documents revealed Mr Donohoe initially rebuffed a request from Ms Fitzgerald last May for funding so the project could be brought forward by two years.
In the letter, released under the Freedom of Information Act, Ms Fitzgerald said the chronic shortage of space at Forensic Science Ireland's facility at Garda Headquarters was greatly hampering its work.
"In short, the potential risk of contamination of DNA samples has led to a greater amount of staff being devoted to checking and double-checking that no contamination has taken place," the Tánaiste wrote.
This, she said, had "greatly impacted on service delivery".
The letter outlined how the laboratory was so stuck for space it was using areas on the stairwell and near elevators, but was being forced to vacate these due to fire safety regulations. Ms Fitzgerald also said the laboratory lacked the facilities for the sharing of DNA information under EU anti-terrorism laws.
In a separate letter prior to the Budget, Forensic Science Ireland director Sheila Willis told a senior Department of Justice official the drawbacks of the existing facility had been well documented.
"This has become more acute in recent times because the increased sensitivity of the DNA chemistry used means that we can detect lower and lower levels of DNA.
"It allows better case results but also calls for increased precautions in avoiding inadvertent contamination," she wrote.
In a statement, the Department said extra accommodation would be found for Forensic Science Ireland while construction takes place on the Backweston facility.