Spain has approved draft legislation for fines of up to €30,000 (£25,000) for offences such as burning the national flag, insulting the state or causing serious disturbances outside parliament.

Opposition parties, judicial and social groups have heavily criticised the bill as an attempt by the conservative government to muzzle protests against its handling of the severe economic crisis.

The measures, presented by the interior minister Jorge Fernández Díaz to update a 1992 law, also include fines of up to €1,000 for insulting or threatening police officers during demonstrations. Similar fines are planned for disseminating photographs of police officers that endanger them or police operations.

Spanish cities have experienced weekly protests, the vast majority of them peaceful, since the start of the crisis in 2008.

The conservative Popular party took office with Mariano Rajoy as prime minister in 2011 and issued a series of austerity measures and cutbacks in health and education and labour and financial reforms in an effort to refloat the economy and stave off a bailout.

The measures triggered an increase in street protests, including several attempts to encircle parliament, some of which ended in clashes with police and rubbish containers being set on fire.

"When more than 20% of people are unemployed, I don't think this legislation is what we require," said Alejandro Touriño, partner and information specialist at the law firm Ecija.

The draft legislation for the most part does not define new infractions or offences, but lays down guidelines for fines that judges will be able to impose. Until now, it was up to a judge to decide the level of a fine.

It does, however, include four new offences, which are classified as very serious and could carry fines of up to €600,000. They are: demonstrations that interfere in electoral processes; unauthorised or prohibited protests at strategic installations such as airports or nuclear plants; and aiming blinding lights – such as laser beams – at public transportation. Any person who commits three lesser offences within two years will also be in line for a maximum fine.

The bill must be approved by parliament, but its passage is virtually guaranteed as the ruling party has an absolute majority in both chambers.