The changes to the archives act, passed in parliament in January but not yet in force because of the SDS's referendum initiative, are said by the government to make access easier, while the opponents claim that the archives are in effect being closed down after the SDS-led government opened them up in 2006.

In the centre of the dispute is the expansion of restrictions governing access to sensitive personal data (sexual orientation, religion or health problems) of victims of organisations such as the Communist-era secret police and other state organisations to that of members of these organisations.

While the government argues this is required by human rights standards, the SDS and several researchers claim the censoring of this data will take so much time as to prevent any serious research. The opponents have been arguing that this amounts to "equating victims with perpetrators".

Turnout will be a key element in Sunday's referendum, as last year's changes to referendum rules require that at least one fifth of all qualified voters need to vote against a law to be defeated.

Given relative low referendum turnouts from the past, and the paltry turnout in the recent Eurovote, this could prove a difficult feat to accomplish for the SDS, as just over 343,000 voters need to vote against the changes to prevent their implementation.

In counting the votes, the National Electoral Commission will therefore first count whether the majority of those who cast the votes voted against the law; in that case it will then determine whether the no votes represent a fifth of the electorate.

Both conditions need to be fulfilled for the law to be repealed.

Polls will be open between 7 AM and 7 PM. The National Electoral Commission is not expected to release first results before 9 PM local time.