Shocked opposition parties in Ireland were told on Tuesday that more than $15 billion in savings must be retrieved from somewhere before 2014.
This figure was previously thought to come in around $10.5 billion.
"The figure of adjustment published in the government plans was 7.5 billion euros ($10.5 billion). With lower growth rates projected, the level of adjustment is going to be significantly higher than that," Michael Noonan, finance spokesman for opposition party Fine Gael, told reporters on Monday.
The revelations came during a briefing from senior financial figures on Tuesday as they pave the way for a four-year budget plan expected to be released in the next few weeks.
Finance Minister Brian Lenihan, who is battling cancer, has already said his government must find savings "well-above" the estimated $4 million already stated.
The opposition parties all agree that its essential for the government to get their budge deficit below the EU limit of three percent by 2014.