Lib Dems pledge to halve London morning commuter fares
London mayoral candidate Caroline Pidgeon has promised if she is elected in May she will cut Tube and rail fares for journeys before 07:30 by half.
The Lib Dem said the move would help London's lowest-paid workers.
Labour's Sadiq Khan has pledged to freeze fares until 2020, and Conservative Zac Goldsmith has said he would "bear down" on travel costs.
Green candidate Sian Berry wants to scrap travel zones and introduce a flat fare across the city.
The Lib Dems' proposed change would apply to all trips using the Underground, Docklands Light Railway, Overground or TfL rail which start before 07:30.
Ms Pidgeon said it "would really help some of London's lowest paid workers who often have to work unsocial hours" and claimed it was "a genuine fare cut that can be delivered immediately".
'Disproportionate' fares impact
Travel watchdog London TravelWatch published a report last month which found London's low-paid workers "are being disproportionately affected by rising transport costs".
It found those on lower incomes tend to spend longer travelling to work and pay more for travel as a proportion of their income.
She added it would also help tackle overcrowding, with TfL recording the highest passenger flows during the morning peak in the hour from 08:00 to 09:00.
The Lib Dems estimate the fare cut would cost £30m a year, which they say they would be funded in the first two years by withdrawing the financial support TfL is giving to the Garden Bridge project.
TfL's financial support for the Garden Bridge has been capped at £10m. The Lib Dems said they would also use "other savings identified in TfL's budget".