The bus is currently running on a Sunday service, with additional early morning journeys from Mondays to Saturdays.
Commuters and patients who regularly travel to the hospital have complained about the changes.
One individual who works at Forth Valley Royal Hospital said: “The service has been abysmal for some time and the latest changes have just made it worse.
“While I appreciate the fact they've had to reduce services due to the ongoing driver shortages, it is totally unfair that the essential workers are being penalised”.
Currently, the bus serving the hospital is travelling the full route through Falkirk, meaning a single-decker bus must be used, due to a low bridge.
As a result, the commuter said: “The morning peak services are often packed with passengers even having to share seats which undermines social distancing”.
He suggested the route could be split at Falkirk, and said: “The high demand during the morning peak to and from Forth Valley Royal Hospital can really only be met using a double-decker”.
Social distancing is not legally required on buses, and they can run at full capacity.
Other hospital workers took to Twitter to complain about the changes, with one individual also expressing anger that her driver was not wearing a mask.
A spokesperson for First Bus drivers said that drivers are exempt from wearing a mask as they work behind a protective screen, but noted they will wear one if they need to leave the cab to assist a customer.
He said: “Along with many other organisations up and down the country, we are experiencing a higher-than-normal level of staff sickness due to the current wave of Omicron Covid 19 cases. The safety of our staff and customers will always be our number one priority.
“As a result, we have had to introduce a temporary reduced timetable across our network. The temporary timetable will operate until further notice, but we will look to supplement this with additional peak journeys as and when resource allows.
“We are doing everything we can to minimise disruption to services and inconvenience to our customers and our teams are working extra hard to ensure as many buses run as is possible.
“We are continuing to do everything we can to support and look after our colleagues whilst in the workplace with hand sanitizer, face coverings and enhanced cleaning taking place to minimise the risk of transmission of the virus. Our local teams will continue to ensure our vehicles are cleaned regularly to a high standard.
“We’d like to apologise to all customers who are affected by these timetable changes. For the latest information, we will continue to provide regular updates on services across the Forth Valley through our local website – www.firstscotlandeast.com, the First Bus app and our social media platforms.”