An independent panel has recommended a change in the current shift patterns for London firefighters to "achieve increased productivity".
An arbiter from Resolution Advisory Panel (RAP) gave two options - 11-hour days and 13-hour nights or 10.5-hour day shifts and 13.5-hour night shifts.
The London Fire Commissioner Ron Dobson said he was pleased the arbiter backed "the case for contractual change".
The Fire Brigades Union said it would ballot its members on the proposals.
The union said its regional committee had decided to recommend its members the option of 10-and-a-hour days and 13-and-a-half-hour night shifts.
More than 5,500 firefighters went on eight-hour strikes in October and November and called off a planned 47-hour strike on Bonfire Night at the last minute.
The Fire Brigades Union (FBU) went on strike claiming its members face the sack unless they agree to sign new contracts in which their shift patterns are changed.
Prof William Brown, who chaired the RAP, said: "I believe that there is a case for contractual change.
"But because it is a contractual change I further believe that in this instance employees should be consulted by the union through a robust mechanism on which of the two options is the most preferable."
Ron Dobson, Commissioner of the London Fire Brigade, said: "I am pleased that the independent chairperson of the panel has supported my view that there is a case for contractual change and the two recommendations put forward by Professor Brown now give the FBU the opportunity to put both to their members to decide which one of these options they would prefer."
Brian Coleman, chairman of the London Fire and Emergency Planning Authority, said: "I strongly welcome the proposals."
Ian Leahair, FBU's executive member for London, said: "We welcome the chairman's [Prof William Brown] recognition that all changes to contracts of employment should be negotiated.
"We further welcome he acknowledges that it is for the employees to decide what are the best shifts for them and we will be carrying out a robust and comprehensive balloting procedure."
Currently firefighters work nine-hour day and 15-hour night shifts. The LFB had originally proposed equal 12 hour day and night shifts, changing the offer to 11-hour day shifts and 13-hour night shifts, but this was rejected by the union.