A last-ditch effort to block pharmacies needing to bring in 60-day medicine dispensing is expected to fail.

The opposition is moving in federal parliament to disallow Labor's key health policy, saying while it supports the idea of 60-day dispensing, the implementation would hurt community pharmacies by stripping them of revenue.

But they have failed to secure the crucial support of the Greens, who hold the balance of power in the Senate.

The changes allow script holders to receive two months' supply from one script, effectively halving the cost of medicines.

Opposition health spokeswoman Anne Ruston has moved to have the Senate strike out the policy with a disallowance motion, saying there are real concerns small pharmacies could shut or cut back on staff to cover the costs.

Senator Ruston said the government needed to delay the policy's start date and consult with pharmacists.

"We want to work with the government and with the pharmacy sector and with Australians who rely on pharmacies to make sure this initiative is implemented in a way that they will receive the cost of living savings," she said on Wednesday.

"If the government won't come back to the table, we know it will be older Australians, vulnerable Australians and Australians who live in rural and regional remote areas that will be most impacted by this measure."

But Health Minister Mark Butler slammed the move, saying Australians would miss out on hundreds of millions of dollars of cheaper medicines if the coalition action was supported.

"This is good for the hip pocket obviously ... but it's also good for health as it frees up millions of GP consults that we desperately need for important health conditions, rather than just routine scripts being issued by doctors," he said.

Mr Butler said cutting the policy would also block $1.2 billion in community pharmacy investment by cancelling other associated measures, including the doubling of the allowance paid to rural pharmacies and a subsidised opioid dependence treatment program servicing about 50,000 people.

The Greens will not support the disallowance motion, meaning the opposition will need every one of the eight crossbench members to support it.

The two One Nation senators and former Liberal turned independent David Van have put their names to the motion, leaving two Jacqui Lambie Network senators and independents Ralph Babet, David Pocock and Lidia Thorpe as final arbiters.

The disallowance motion is set to come before the Senate on Thursday.