An 11th-hour intervention by the government last week averted a 24-hour shutdown of many of the city’s public buses, with 1000 drivers working for operators Transdev and CDC preparing to walk off the job.

It is understood that the peace deal came at the cost of millions of dollars from Treasury coffers over the next three years.

All the parties to Wednesday's last-minute deal to avert the strike were tight-lipped about what exactly was put on the table.

But sources close to the talks have told The Age that the government agreed to underwrite the $1800 one-off superannuation top-up for each bus driver and 1 per cent of the 4 per cent pay rise won by the Transport Workers Union for its members.

The strike by drivers, whose pay talks were at a standstill, was potentially politically damaging to the government, which faces an election  on November 24.

Buses were set to stop rolling last Thursday on 120 routes or about a third of the metropolitan network.

Public Transport Minister Jacinta Allan and Treasurer Tim Pallas, who helped broker the deal between the two bus companies and their drivers’ union, the TWU, have refused to say what the government offered to achieve the peace settlement.

The in-principle agreement hammered out last week is comparable with the 14 per cent wage increase over four years for tram and train drivers, agreed in 2015 following strikes.

The average bus driver is paid between $50,000 and $60,000 a year, and the government intervention could cost taxpayers more than $3.5 million over the three-year life of the deal.

Transdev operates 30 per cent of Melbourne’s bus network and CDC Victoria runs about 17 per cent of Victoria’s bus services.

Ms Allan’s office would not provide details of what had been promised, saying the details of the settlement would remain under wraps until the bus drivers voted on Wednesday to accept or reject the agreement.

The action would have shut down 120 bus routes, and one-third of the metropolitan bus network.

Ms Allan’s office declined to answer questions on Sunday about the detail of the deal but provided a statement.

“Recognising the impact industrial action would have had on passengers, the government has been working with both parties over the past few days,” a government spokesperson said in the statement.

“We are pleased all parties returned to the table to reach this resolution.”

TWU branch secretary John Berger did not respond to a request for comment, but in a bulletin sent out to bus drivers, the union leader warned other Victorian bus operators.

“The job is not complete,” Mr Berger wrote to his members. “The TWU will now be focusing on bus operators that have a strong TWU membership that are willing to fight for a better deal.”

Transdev did not answer inquiries on Sunday.

A CDC spokeswoman declined to confirm details of the deal, referring questions back to the government.

“The package includes an industry-leading set of benefits and a wage agreement that recognises the important role our bus drivers play," she said.