A leading lawyer has claimed that Scotland's deposit return scheme could create an unlawful trade barrier with the rest of the UK.
The initiative is due to launch in August and is designed to boost recycling via a 20p deposit on single-use drinks bottles and cans.
But Aidan O'Neill KC said the Scottish government may have to delay it until the launch of a UK-wide scheme in 2025.
He made the remarks in advice sought from a group of distillers.
The Scottish government said it would continue to "work closely" with the other administrations across the UK.
Critics of the scheme in the drinks industry have voiced concerns that it will disrupt trade, create higher prices and reduce choice.
Fears bottle return scheme will not be ready
Under the initiative every drinks producer based in Scotland will have to add 20p to products to be sold in the country in a single-use container.
It will be charged to the retailer who will in turn bill the consumer.
In order to recoup this money people need to take the empty bottles or cans to a reverse vending machine in a supermarket or designated return point.
A total of 17,000 return points have to be set up across Scotland, with the scheme due to go live on 16 August.
In a legal opinion, Mr O'Neill said he believed there were "well-founded" concerns that the scheme would create a trade barrier between Scotland and England as it would require different prices to be charged for the same product on each side of the border.
He said expert economic evidence would be required to confirm this, but that it meant the scheme could contravene the UK Internal Market Act 2020.
Mr O'Neill also warned that the regulations could not be enforced for single-use packaged drinks imported into Scotland from elsewhere in the UK, which would disadvantage Scottish producers.
He said this should "not come as any surprise to the Scottish government" as the Scottish Parliament was warned about such potential legal difficulties in a 2020 briefing paper by a University of Cambridge law professor.
The UK government said its preference would be to launch a UK-wide deposit return scheme as it would "minimise disruption to the drinks industry and ensure choice for consumers".
A spokesperson added: "As the Scottish government is pressing ahead with their own deposit return scheme, the UK government is working with them to ensure as much interoperability as possible between the schemes across the UK."
A Scottish government spokesperson said: "We continue to work closely with the other administrations in the UK to ensure that Scotland's DRS is as closely aligned as possible with other potential schemes in the UK."
