New laws to sell cigarettes in plain packets are set to pass parliament after the coalition swung behind the Gillard government move.

Opposition Leader Tony Abbott said the coalition would not oppose the laws when they were presented to parliament later this year, but would propose a number of amendments.

However, if the amendments - which Mr Abbott did not spell out in detail - were not carried, coalition MPs would allow the bill to pass.

"There was a short discussion of this issue in the shadow cabinet yesterday and there was a discussion in the party room," he told reporters in Canberra today.

"We will seek to amend the legislation to ensure it really does bring smoking rates down."