UK ports will be plunged into "chaos and confusion" in the new year unless post-Brexit lorry parks are completed, a union has warned.
Unite also said new online border checks would lead to delays at ports.
The government denies the union's claims that most of the planned lorry parks will not be ready if needed after the UK's transition phase with the EU ends on 31 December.
The Cabinet Office said £705m was being spent preparing the UK border.
The government has given itself powers to grant emergency planning permission for temporary lorry parks and inspection posts in 29 councils areas across England, without the need for local approval.
Areas affected under the powers include Cheshire, Lincolnshire, Liverpool, Devon and East Sussex.
Unite national officer Adrian Jones said: "With less than four months to go, the locations of the vast majority of the lorry parks have still not been announced, let alone built."
A Cabinet Office spokeswoman said: "All the transit sites prepared in Kent for a potential no deal last October are already in place and will be stood back up."
The government said it was "confident that all the sites and infrastructure will be in place when they are needed in 2021 after the transition period ends".
After 1 January 2021, traders will need to fill in Smart Freight online customs declaration forms, allowing them to ensure their goods are ready for border checks before they set off for ports.
The system will be ready for January 2021, the Cabinet Office said
Mr Jones said Unite was concerned how it would operate in practice for lorry drivers.
The union said it was "completely unacceptable" that lorry drivers faced being personally liable for £300 fines if they were found to be travelling to the ports without the correct electronic documentation.
"Drivers are also facing the increasing likelihood of being stuck in their cabs for hours on end without adequate access to clean toilets, washing, food or rest facilities," Mr Jones said.