Lakeside Coaches, the Shropshire transport company based at Ellesmere, posted about the shocking incident on its social media page.
The firm revealed that a person had thrown something at the windscreen of one of its coaches from a bridge above in Shrewsbury, late on Wednesday evening.
The object cracked the windscreen, causing £3,000 of damage.
The firm said it was fortunate that the driver had managed to maintain control of the vehicle – and had only just dropped off his passengers at the time.
Posting on social media last night the company said: “This is the newest vehicle on our fleet, at just three weeks old it is now out of service due to one idiotic individuals behaviour.
“Last night at 22:54, this individual wearing a blue T-shirt and shorts standing on Monkmoor Road bridge over Robertson Way decided to throw something (hard and heavy) off the bridge at our coach causing £3000 worth of damage.
“The vehicle was scheduled to take a school to London today but is now off the road until a new windscreen is shipped and fitted-estimated five days lost earnings.
“Thankfully our driver kept the vehicle under control and he had just dropped off passengers, covered in glass shards and a minor cut to his hand we are glad the outcome was not a lot worse!
“Any information or footage relating to the incident would be greatly appreciated (confidentially).”
West Mercia Police have confirmed they are investigating the incident with a spokeswoman saying: “At around 11.20pm on Wednesday 26 June we received a report that a coach had been damaged on Robertson Road after something was thrown at it from a bridge. Enquiries are ongoing.”
People can contact the firm through its facebook page or its website (https://lakesidecoaches.co.uk/).