National Express West Midlands bosses accused strikers of blocking buses leaving several garages in Coventry and Birmingham on Wednesday morning,while union Unite has accused the bus operator of "unjustly calling the police to peaceful picket lines" and "threatening striking workers with job losses and route closures".
Union bosses said a free phone hotline on 0808 164 0368 had now been launched for workers to report "instances of intimidation" in relation to the dispute.
The union has claimed workers have reported being told they will be barred from overtime in future because they have gone on strike.
National Express has said it has committed to running every bus possible during the strikes, with a skeleton service in place.
The operator said police had been called after buses were prevented from leaving garages in Coventry and Birmingham.
A National Express West Midlands spokesperson said: “We are grateful to the police for their support this morning.
“We fully respect the rights of bus drivers to withdraw their labour and picket their workplace, but they should not be blocking buses from departing garages.
“The people of the West Midlands are being disrupted enough by these strikes, but to prevent even a skeleton service is completely unacceptable.
“We are in dialogue with the union about our offer of a 14.3 per cent pay increase to our drivers, which, at £16.46 an hour, would take the typical driver to £33,000 a year, and our door remains open for talks.”
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.
The union said the offer was a 'real terms pay cut' while the company makes considerable profits.
On Monday, bus drivers began indefinite strike action – which will continue until the situation is resolved.
There have also been picket lines outside National Express garages in the Black Country, including in Wolverhampton and Walsall.
Unite general secretary Sharon Graham said: “Our members are rock solid in their determination to win a pay rise that reflects the difficulty of their roles and soaring living costs. They know that National Express can absolutely afford to pay it.
“The company’s bully boy tactics to break the strike will only result in worsening the dispute and Unite will make sure National Express is held fully accountable for any intimidation of our members. There is only one way to end this – National Express must put forward an offer that is acceptable to our members.”
Unite national lead officer Onay Kasab said: “Our members do not want to strike but have been forced to by the company, who bear full responsibility the for disruption being caused. National Express can afford to put forward a fair pay offer and that is what needs to happen.”
Bus drivers in the region have reported facing regular abuse on the job.
One said: “I’ve had bricks thrown at my bus, and I’ve had lads spray paint all over my bus and even in my face. I’ve had to take time off work for that.”
Another said: “I’ll be at work for 12 hours, drive nine of those but because of the way pay is worked out I’ll get wages for just seven and a half hours.
"It’s split shifts so I can start work 4am one day and on another I’ll be finishing at 10pm.
"A lot of the time, I’m driving continuously for five and a half hours and there’s no access to a toilet. No wonder there’s always a shortage of drivers.”
People are encouraged to check the nxbus.co.uk website to confirm which services are running.