The European Union's executive arm gave few details about the deal, which emerged on Friday, saying it needed unanimous backing from the EU's 27 finance ministers.
The Commission said that when assessing whether a country should face EU budget discipline steps, the EU executive would take into account whether the state had carried out pension reform.
"The assessment would be carried out on a case-by-case basis. It will take into account whether the [budget] deficit is justified by systemic pension reform," Commission spokesman Amadeu Altafaj told a regular news briefing.
Commission President José Manuel Barroso and Polish Prime Minister Donald Tusk clinched the deal by telephone late on Friday. Barroso will send a letter to Tusk with details on Monday or early on Tuesday.
Polish officials have said the agreement would allow Poland to have a budget deficit of up to 4.5% of economic output, 1.5 points more than the official ceiling, without facing the EU's disciplinary steps.
Altafaj would not confirm the figure and said that to count on leniency, a country's public debt must be below 60% of gross domestic product.
As part of its reform from late 1990s, Poland is transferring sums worth up 2.5% of GDP annually to private pension funds which invest them in securities, mainly Polish treasury bonds.
EU disciplinary steps could in principle lead to fines for eurozone members and freezing some EU aid for other countries of the bloc.
EU governments are working on tightening the rules to prevent budget deficit overshoots such as that of Greece, which sparked investor worry about the stability of the euro zone.
EU leaders are expected to discuss briefly the pension issue when they meet in Brussels on 16-17 December and the debate will continue at finance ministers' meetings early in 2011.
Poland and other budget reformers have fought for permanent fiscal leeway, but Altafaj said it will only be temporary.
Warsaw says its proposal would encourage other countries to carry out reforms that are necessary because of their ageing populations, but which have provoked protests in some cases.
Hungary seizes 10 billion euros of private pension funds
In the meantime, Hungary effectively dismantled its pension reform. Hungarian lawmakers voted to roll back a 1997 reform of pensions on Monday, effectively allowing the government to seize up to 10 billion euros in private pension assets to cut the budget deficit while avoiding austerity measures.
Parliament passed the pension legislation with 250 votes for, 58 votes against and 43 abstentions. Orban's ruling Fidesz party has a two-thirds parliamentary majority.
The legislation imposes stiff penalties on Hungarians who do not transfer their pension assets back into the state system by the end of January.
The government will sell the assets and use the income to cut debt, plug holes in the state pension fund and create room for tax cuts for households and small companies.
By plugging its budget shortfall with the pension funds and new taxes on banks and mostly foreign-owned businesses, Orban has promised to end years of austerity and bolstered the popularity of his right-of-centre Fidesz party in opinion polls.
But the strategy - which also includes regaining "financial sovereignty" by ending a 20 billion euro safety net deal with the European Union and the International Monetary Fund - has worried investors, caused losses in Hungarian assets, and prompted a downgrade by Moody's ratings agency last week to Baa3, the lowest investment grade.
Economists say that by raiding private funds, Orban will cut the deficit to below 3% of gross domestic product next year. But he will also only delay reforms which they say are vital to tackle a debt pile equivalent to 80% of GDP - just above the EU average but higher than any other country in the bloc's post-communist East.
(EurActiv with Reuters.)