Opposition Leader Tony Abbott says the Coalition will not oppose plain cigarette packaging legislation.

Mr Abbott has repeatedly said the Opposition will not make a decision about plain packaging until it sees the bill.

But he says the Opposition has not changed its position "because we didn't have a position as such".

"Nevertheless, there was a short discussion of this issue in the shadow cabinet yesterday. There was a discussion in the party room," he said.

Mr Abbott says the Opposition will attempt to amend the legislation to ensure smoking rates really will decrease.

"But if our amendments fail, we won't be opposing the legislation," he said.

He did not outline what the amendments would be.

The Government has been attacking the Opposition every day in Question Time over the issue, but Mr Abbott denied he was moving to defuse a damaging political problem.

"We will do what we can to ensure this legislation is effective in bringing smoking rates down, but if amendments we move are not successful, then we won't be opposing it," he said.

Federal Health Minister Nicola Roxon has praised the Opposition's stance, but says Mr Abbott had to be convinced.

"There were many members on the Liberal Party backbench who finally brought the Leader of the Opposition to this position," she said.

"It was against his instincts. His instincts are to say no. He didn't want to do it but he has been forced to do it by the weight of evidence that this is the right thing to do."