Drivers voted by 71 per cent against National Express West Midlands' 14.3 per cent pay rise after the offer was put forward in a ballot over Friday and Saturday.
It means more than 3,100 members of the Unite union will walk out on Monday for indefinite strike action – which will continue until the situation is resolved.
Unite general secretary Sharon Graham said: "National Express is an extremely wealthy company and makes considerable profits from the hard work of our members, who are not paid enough for the difficult and stressful job they do. The company must come back with an offer our members can accept.
"Unite’s top priority is defending and improving our members’ jobs, pay and conditions and National Express’ workforce have their union’s full support during these strikes."
The result will severely decimate around 93 per cent of the bus network and will impact Wolverhampton, Walsall, Dudley, Sandwell, Birmingham and elsewhere. However it is understood bus routes used by people to get to hospitals in the region will be maintained.
Unite lead national officer Onay Kasab said: “National Express have said time and again that Unite has not allowed our members a proper say on the pay deals they have put forward. The company’s arguments have now been exposed as hot air. The truth is this: National Express drivers have had enough.
“Our members are clear the offer needs to improve to reflect rising prices and the incredibly hard job they do. This will also benefit West Midlands bus services as it will help solve National Express’ recruitment and retention problems.”
A bus driver, who wished to remain anonymous, told the Express & Star: "Drivers are in solidarity with the result. Many are fed up with how National Express West Midlands does not give them the recognition they feel they deserve, with regards to pay and all the grief they get daily just doing their job – and how (the company) has badly handed the negotiations.
"They strongly feel they are worth more than is being offered, they want a bit more but are not greedy at all. As well, it is about finally having the chance to legally stand up for themselves, because they are in a union they can do so in a way that doesn't mean they face a disciplinary for doing so."
Union chiefs highlighted reported revenues by National Express, which runs bus and coach services, which increased by 29 per cent to £2.8 billion whilst underlying profits more than doubled to £197.3 million.
National Express West Midlands confirmed a limited service – primarily serving the region's major hospitals – would operate on Monday. Meanwhile they have told passengers to expect disruption to buses from around 10.30pm on Sunday.
A spokeswoman said: “We are sorry for the disruption that this will cause across the West Midlands. Our advice to customers is not to try to travel on our buses unless you really need to. As the week goes on, we hope to add back in more services so please check our website for the latest information.
“We are working with our partners to minimise the impact of the disruption in any way we can and we are seeking to bring a speedy resolution to the strike.”
The company said the rejected offer included a 14.3 per cent pay increase, along with increases to Christmas and New Year's pay and accident pay. It would have brought an experienced driver salary up to almost £33,000 and "unlocked" more than £900 of back pay for a full-time driver.
Business leader Ninder Johal, who is the chair of the Wolverhampton City Investment Board and previously a board member of the Black Country LEP, said: "Transport and transport infrastructure is key to the functioning of an efficient economy. People need to be able to go to and come back from work and use buses to collect children and for essential services.
"Buses are a key ingredient in any economy's transport system and it will damage productivity and output of the economy, which is already trying to recover from the cost of living.
"Now it might not be as damaging as in the past, because some people still work from home. But we need an efficient working transport system for the benefit of all. I hope the dispute is brought to a rapid conclusion."
Meanwhile chiefs from Diamond Bus said services would be unaffected by any strike action, but they were expecting a much busier day on Monday.
A spokesman said: "Diamond Bus, wishes to reassure our passengers that Diamond Bus services will not be affected by the strike action and will continue to operate as normal.
"For those National Express customers who will be affected by service disruption, Diamond provides a wide variety of regular bus services across the West Midlands, and we advise you to check our website for alternative services that may enable you to continue to your travel requirements and complete your essential journeys."
On Friday evening, the bus operator said engineers had voted to accept the new offer of a 14.3 per cent base pay increase along with another 3.5 per cent rise next year. In 2024, should the consumer price index (CPI) reach four per cent or above in December 2023 the company will reopen negotiations with unions.