Ljubljana - The opposition Democrats (SDS) will be collecting signatures for a referendum with which they want to challenge government expansion by three departments in autumn, the parliamentary speaker's office said on Tuesday.

The SDS will have between 1 September and 5 October to collect 40,000 signatures, a requirement for a referendum with which they want to prevent Prime Minister Robert Golob from expanding his government to 20 departments.

This is a second attempt by the SDS for a referendum on the changes to the government act, which Golob's emerging coalition filed to parliament in May.

After their motion for a consultative referendum was voted down by the coalition on 21 June and the National Assembly passed the changes a day later, the SDS decided to challenge the new law in a legislative referendum.

The party first collected 5,000 signatures in the seven days after the law was passed, which must be followed up by the collection of the 40,000 signatures needed for parliament to vote whether to call a referendum.

This step usually takes place soon after the first collection of signatures, the only exception being the summer break. Referendum legislation stipulates that if the process falls between 15 July and 31 August, the collection should start on 1 September.

The SDS hopes that the referendum would be carried out alongside the presidential or local elections, both coming up in autumn.

The biggest opposition party believes the planned government expansion would be too costly and has said that the main reason for its referendum efforts was "the unbelievable mess" the government made in face of growing fuel prices.

If the SDS succeeds in the referendum, the National Assembly will not be allowed to pass a law going against the referendum decision for a year from.