Zeljko Reiner of the Croatian Democratic Union (HDZ) said the executive authority would become stronger, while parliament would only endorse its decisions.
Branko Vuksic of the Labour Party said parliament was a cover for the government's bad moves and that MPs were to blame because they allowed themselves to be manipulated.
Reiner said it was sad that the bill was being discussed two weeks before Croatia's European Union accession.
Davorin Mlakar of the HDZ criticised the government for not sending someone to the discussion.
Speaker Josip Leko said the government had voiced its position on the bill in writing.
Reiner said the prime minister should report to parliament on European Council sessions at least four and not two times a year.
Pedja Grbin of the ruling coalition's Social Democratic Party (SDP) said the government acted in EU institutions based on a conclusion if adopted by parliament. He added that if parliament's conclusion was different from the government's position, the government must act on the former.