Plans to introduce a deposit return scheme in Scotland are too complicated and could miss a planned 2021 launch date, experts have warned.
The Scottish government will add 20p to the cost of some plastics, cans and glass as part of its climate action plan.
It is hoped the scheme will be up and running by 2021.
But the government's own advisory group has "raised concerns" about "deliverability on that timetable".
Legislation to enable the changes, which will see 20p added to the price of a single-use drinks container bought from a shop, is expected to be unveiled by ministers when the Scottish Parliament returns from its summer recess next month.
About 40 countries worldwide - including Germany and Sweden - operate deposit return schemes and the Scottish government has said it is confident Scotland can successfully follow suit.
The decision to include glass in the recycling initiative has been one of the main sticking points, according to minutes of the June meeting of the Scottish government's deposit return scheme implementation advisory group, which includes retailers, producers and environmental groups,
The report states that a phased approach to implementation would see the legislation passed and a scheme operator appointed by April next year, with a further period of at least 12 months before the scheme is up and running.
On this programme, the minute recorded: "The group raised concerns regarding the deliverability of the scheme on that timetable and highlighted that these concerns were exacerbated by the decision to bring forward a scheme which, due to the inclusion of glass, was more complex and costly than it may otherwise have been".
Andy Tighe, policy director of the Scottish Beer and Pub Association, and a member of the advisory group, told BBC Scotland that a timetable which aimed to get the scheme fully operational by the spring of 2021 is "highly unrealistic".
He said: "There is no change in our support for the waste reduction principles behind the scheme but many of us around the table trying to work on the implementation are concerned about the timescale and unintended consequences of the scheme.
"The inclusion of glass has made it a lot more complicated, it will lead to higher processing costs and it is hard to see a scenario where these costs will not be passed on to the consumers.
"Both industry and consumers want a system that is simple and we still have time to take stock and look at a joint system with the rest of the UK, or at the very least a compatible one.
"We think it would be sensible to hold off naming a final launch date as such until all of the issues are ironed out."
A Scottish government spokeswoman said: "We continue to make progress with our plans to implement a deposit return scheme as part of our response to the global climate emergency.
"Recent research by Zero Waste Scotland indicates strong public support for including glass in the scheme and the wider benefits are clear, including increased recycling rates, reductions in carbon emissions and reductions in glass litter.
"We are aware some businesses have concerns about its inclusion and we are committed to working with them to implement the scheme in a way which addresses those concerns."
How will the scheme work and how will I get my deposit back?
Effectively, 20p - the deposit - will be added to the price of a single-use drinks container bought from a shop.
The consumer will get their deposit back when they return the empty bottle or can to the retailer.
All types of drinks and all containers above 50ml and up to three litres in size are included.
Businesses selling drinks which are opened and consumed on site - such as pubs and restaurants - will not have to charge the deposit to the public.
There will be two ways you can return your empty container - over the counter, or by using a reverse vending machine (RVM).
An RVM is a machine that scans containers when they are returned and then refunds your deposit.
The government says there will be a range of ways you can get your 20p back, for example cash at a till, a token or discount voucher or digitally. The returned containers are stored in the machine and are then collected for recycling.
As well as retailers and hospitality businesses, schools and other community hubs will be able to act as return locations.
Scotland is likely be the first nation in the UK to introduce a bottle deposit return scheme but a consultation is taking place in England where a deposit of 15p is being mooted.
The Scottish scheme will cover all single use cans and bottles, including every individual item in a multipack.
More details about the scheme are expected to be announced next month.