It came as the Scottish Greens highlighted their election manifesto pledge for a Scottish rail card to enable everyone to get one third off ScotRail fares.
The Greens have already won a pledge from the SNP to extend free bus travel from the under 19s which is due to be introduced this year, to all under 22s.
The party wants this further raised to everyone under 26, followed by a similar move for rail travel, along with free ferry for young people.
Scottish Labour today backed free bus travel for the under 25s at the launch of its manifesto.
It stated: “We will extend free bus travel to under 25s, with a long-term goal of working towards universal free bus travel.”
The Poverty Alliance is leading the call for other parties to follow suit, backed by organisations such as Friends of the Earth Scotland, the Scottish Youth Parliament and Barnardo’s Scotland.
It said other people, such as those on Universal Credit and low-income benefits, should also qualify for free bus travel.
Scottish Greens co-leader Patrick Harvie told The Scotsman today: “If you do this right, these policies can pay for themselves.”
He said it would also help retain bus routes which might otherwise be scrapped.
"Those routes can be viable if you’re subsidising a bigger proportion of the passengers with a collectively-funded scheme that’s paid for through taxation.
"Subsidy is not a dirty word when we talk about something that benefits us all.”
The Poverty Alliance coalition said free bus travel would be “critical in stemming the rising tide of pandemic-related youth unemployment, with bus travel particularly important for young people and people on low incomes to help them access the labour market.
"Without this action, they risk being left behind in our economic and social recovery.”
Director Peter Kelly said: “This move would also help advance gender equality, as women disproportionately rely on public transport to access jobs, healthcare and activities to boost their well being.
"Lone parents, who are predominantly women, would particularly benefit.”
Mollie McGoran, a member and trustee of the Scottish Youth Parliament, said: “Young people and people on low incomes have been some of the hardest hit by the Covid-19 pandemic and so must be put at the heart of the recovery.
"Young people feel bus fares are too high.
"The cost of public transport creates barriers to participation which are denying young people and those on low incomes access to opportunities.”
Paul White, director of the Confederation of Passenger Transport UK – Scotland, which represents bus operators, said: “The bus sector is open to working with the Scottish Government to examine extending free travel.
"Free bus travel essentially means government reimburses operators for providing each journey – free travel is a subsidy to individuals, not bus companies.
"As with existing concessionary schemes, bus operators should be no worse off for participating.
“Increasing bus patronage is a shared goal we’re happy to contribute to.
"However, it is critical that free travel does not reduce operator revenue, thereby putting bus services and jobs at risk, increasing commercial fares or slowing investment in zero emission vehicles.”