Bulgarian Parliament received on Monday the 560 000-strong petition calling for referendum on election rules.

The list, reportedly containing over half a million signatures, made its way to Parliament's building with a rally in the center of the capital Sofia, repeating their earlier demand that a national poll on the issue be held simultaneously with May 25's European elections, DARIK radio has reported.

Under Bulgarian law, a threshold of 500 000 signatories means that a holding a referendum is mandatory.

Parliament, however, has a few months at its disposal to verify the authenticity of the petition and set a date on which it is to take place.

The petition was allegedly "complete" last week, but the activists explained they wanted to generate a "signature reserve" to avoid a nullification on technical grounds. 

The referendum petition calls for a national poll on three key voting questions: the introduction of a majority election, compulsory voting, and e-voting.

It was proposed in January by Bulgarian President Rosen Plevneliev, amidst preparation of the new Election Code that was already under way in committees within Bulgarian Parliament.

With his move, President Plevneliev divided the opinion in Bulgaria, with some seeing it as a veto on the new legislation and others as part of the infighting between the government and the head of state.