The government's controversial pension levy on public servants is in danger of being found to be incompatible with EU accounting rules – and the government may be wrong in describing the measure as a "pay cut", EU documents show.

While the EU is unlikely to block the measure, the government may be forced to recategorise the levy as a tax and a revenue-raising step, instead of the spending reduction it has been portrayed as.

Public servants had been due to take strike action tomorrow and these problems over the EU accounting rules will give their campaign a boost. The public-sector unions claim the measure is being selectively applied to one part of the workforce and falls disproportionately on lower-paid civil servants.

However, the government argues that the levy is a pay cut for public servants and the measure has one benefit – it does not change the essential pension entitlements of public servants.

The European Commission, in a document sent to Irish authorities last week, says the following: "It is not clear whether that recording is compatible with the ESA accounting rules." The ESA rules are those used across the EU.

"As usual, this technicality will be discussed between statisticians, before Eurostat decides on which accounting option is consistent," the document says.

Eurostat, the EU's statistical body, may force the government to amend its budget and move the pension levy from one side of the ledger to the other. However, the government will be confident of the EU seeing the measure as one that reduces Ireland's crippling budget deficit.

The levy works as follows: a person on €15,000 gross earnings pays a levy of 3% or €450 a year. This rises to 5% on a salary of €25,000 and, in a number of further stages, to 9.6% for somebody earning €300,000. A number of semi-state companies are not covered by the levy and neither are the judiciary or President Mary McAleese.