The changes are designed to stymie attempts by organised crime syndicates to farm out their production to small-scale, individual drug manufacturers in the ACT.

The government's bill, expected to be debated and passed in the Legislative Assembly on Tuesday, means those caught with precursor substances will need to prove they were only making drugs for personal use, and not to sell. That has drawn the ire of the Greens, who say it has removed the presumption of innocence, one of the most important principles of criminal law.

But the government says the burden of proof will still fall largely with prosecutors, who must prove the person had intentional possession of precursor chemicals, and was intending to manufacture drugs.

Attorney-General Simon Corbell said the amendments would close a loophole in the law that had made it difficult to enforce some drug-trafficking offences.

''The government's view is that if the accused is only manufacturing for their own consumption, then it will be easy for them to prove that,'' Mr Corbell said.

''We believe this is a proportionate and reasonable provision, it's similar to provisions in other jurisdictions,'' he said.

The laws are expected to pass with the support of both the government and the opposition.

But the Greens fear the amendments breach human rights laws, and are urging both the government and the opposition to reconsider the move.

Greens MLA Shane Rattenbury said the laws would only target ''small players'' and would do nothing to seriously tackle major, organised drug trafficking.

''We can see a realistic scenario where some teenager gets on the internet, gets the recipe for an illicit substance, has all of the precursors, and under this law can be deemed intending to sell those drugs,'' Mr Rattenbury said.

''They end up with a very serious indictable offence on their record, which is not proportionate to the actions they were undertaking,'' he said.

''That's done out of teenage experimentation and naivety, and the consequences really don't match the crime.'' Mr Rattenbury predicted the laws would likely be found to be in conflict with the human rights laws in the ACT Supreme Court.

He said he had received letters of concern from the ACT Law Society and the Human Rights Commission.

Mr Corbell said he had been approached by the Office of the Director of Public Prosecutions, which had stated a desire for such

changes to the law. ''What we do know is that there is an increasing trend for organised crime to spread its risk by using a large number of people each producing small amounts of illegal drugs,'' Mr Corbell said.

''So we're trying to respond to circumstances where organised crime farm out the production of methamphetamine-type products. That clearly is a trend that needs to be addressed.''

A Canberra Liberals spokeswoman confirmed the opposition would support the proposed amendments on Tuesday.

Discussion of the bill in the Legislative Assembly has already been postponed twice.