Fuel tanker drivers have been urged to reject a deal which was hoped to bring the ongoing threat of strikes to an end.
Unite union leaders have recommended that their members reject the latest proposals on the table in the bitter dispute over conditions.
The move has increased fears of a nationwide strike which could lead to fuel shortages at the petrol pumps.
The dispute centres on what unions call a "turn and burn" culture, with shorter delivery times.
Tanker driver's jobs have been seconded out from major oil companies to other firms, which unions say has left the industry fragmented.
They are calling for national standards to be introduced, something employers say is impractical.
Unite leaders say negotiations have made significant progress on health and safety issues, but progress still needs to be made over pensions.
Drivers have until May 11 to decide how they will vote.
Rules say the union needs to give seven days notice of an impending strike, which means any industrial action would happen mid-late May at the earliest.