The call came after trade unions from across South Yorkshire and the Humber met in Hull for the region’s TUC conference.
The vote in favour of the 100-day pledge was passed unanimously following a similar vote in 2021 which led Tracy Brabin, West Yorkshire Mayor, to begin the bus franchising process just 50 days after she was elected.
About £5m would be spent by the council on assessing the franchising model and its development, but ‘further substantial costs’ will be incurred if the nod is given.
Delegates said the private model in South Yorkshire ‘has failed’ and it was now time to ‘act for people, not profit’.
TUC campaigner Gareth Forest said: “Unions have spoken with one voice and our demands are clear - it is high time we took South Yorkshire’s buses back into public control.
“We’ve had a bus review, we’ve had an informal assessment from the South Yorkshire Combined Authority - bus drivers and passengers need a decision, and they need it fast.
“The new mayor could kick off their term by taking bold action on the most pressing issue this region faces - our crumbling transport infrastructure.
“Trade unions are looking forward to working closely with the new mayor on fixing our transport crisis.
“The private model has failed - now is the time to act for people, not profit.”
A document published by the South Yorkshire Mayoral Combined Authority shows from start to finish, bringing in a bus franchise to the region would take three-and-a-half years to fully implement.
Bus operators welcomed a previous review into services, but said franchising or a publicly-owned system is an ‘unnecessary diversion’ and won’t make the system ‘more attractive’.
Union delegates representing bus drivers, transport workers, NHS staff and passengers across South Yorkshire took part in the vote.
Outgoing Mayor Dan Jarvis - who will remain as Barnsley Central’s MP - and the four South Yorkshire council leaders issued a statement of intent earlier this year to look into the ways and means of starting a bus franchise system across the region.
A council report added: “The £5m estimated cost would simply be incurred in doing the development work to implement franchising and does not cover the eventual running and operating costs of any future franchising scheme.
“Of more significance, there are likely to be further substantial costs associated with moving to a franchising model including transition costs, planned improvements to bus services which are currently unfunded and significant additional costs associated with maintaining existing services as a consequence of declining patronage and other factors.
“Based on figures from the Transport for Greater Manchester franchising scheme and other local estimates, these costs could be in the region of £200m over the period of the development and transition phases.
“These would have potentially huge consequences for the council’s budgets, council tax levels and services moving forwards.( “The costs - and time - of the formal assessment would be saved if a decision not to proceed was taken at this stage.
“However, proceeding to undertake a formal assessment would give a greater detail about the costs and benefits as a whole, making for a more informed decision on the impacts for Barnsley.”