The Danish parliament today passed legislation which will give police sweeping powers of "pre-emptive" arrest and extend custodial sentences for acts of civil disobedience. The "deeply worrying" law comes ahead of the UN climate talks which start on 7 December and are expected to attract thousands of activists from next week.

Under the new powers, Danish police will be able to detain people for up to 12 hours whom they suspect might break the law in the near future. Protesters could also be jailed for 40 days under the hurriedly drafted legislation dubbed by activists as the "turmoil and riot" law. The law was first announced on 18 October.

The Danish ministry of justice said that the new powers of "pre-emptive" detention would increase from 6 to 12 hours and apply to international activists. If protesters are charged with hindering the police, the penalty will increase from a fine to 40 days in prison. Protesters can also be fined an increased amount of 5,000 krona (671 Euros) for breach of the peace, disorderly behaviour and remaining after the police have broken up a demonstration.

The Danish police also separately issued a statement in August (pdf) applying new rules and regulations for protests at the climate conference, warning that "gatherings that may disturb the public order must not take place".

Earlier this month, the Guardian published a letter by environmental activists that described the new law as "deeply worrying" and called for the Danish government to uphold their right to legitimate protest.

Tannie Nyboe, a spokewoman from campaigning group Climate Justice Action in Denmark, said the new law was designed to control civil disobedience during the summit. "These laws are a big restraint in people's freedom of speech and it will increase the police repression for anyone coming to Copenhagen to protest. Denmark normally boasts of how open and democratic a country we are. With this law we can't boast about this anymore.

"It will increase the repression of any protester or activist coming to Copenhagen. This law creates an image of anyone concerned about climate change being a criminal, which will of course also influence the general treatment of any activist who comes into contact with the police or other authorities."

A Danish justice ministry confirmed that the laws had been passed today and would come into effect before the climate conference starts on 7 December.