Passengers travelling on the Birmingham Snow Hill line which runs through stations including Stourbridge Junction and Kidderminster have been left facing short-notice cancellations and smaller numbers of carriages on services.
Nearly 15 services on the route have been hit by the staffing shortages, with six reducing the number of carriages on the train by 50 percent capacity on services between Stratford-on-Avon, Stourbridge and Kidderminster.
A West Midlands Railway spokesperson said: "We currently have an increased number of staff unavailable for work due to the ongoing impact of the Omicron variant.
"While we are making every effort to cover as many services as possible, we are urging passengers to check their journeys before travelling in case of short-notice cancellations."
Other lines have also been affected by staff shortages, with six fewer trains running on weekdays between Birmingham and Shrewsbury along the line running through the region.
West Midlands Railway also posted a message on the company website to inform about the ongoing issues the service was facing in terms of staff and drivers.
The message read: "Unfortunately, due to Covid-19 and social distancing constraints, our driver training programme has been severely disrupted with over 25,000 training days lost.
"This has significantly increased the amount of time it takes trainees to become fully qualified train drivers.
"This unprecedented situation has resulted in trains being cancelled at short notice and fewer carriages being available on some services.
"We are also seeing Covid cases rising again among our workforce.
"We always aim to cover as many services as possible through staff working overtime but this is not always possible, particularly at popular holiday times such as school holidays and half-terms."
The issues being faced by passengers in the Black Country and surrounding area are being felt by passengers across the country as Omicron variant-related staff shortages and other faults mount up.
Rail journeys across Britain were also being hit by many operators using reduced timetables in a bid to improve reliability after weeks of short-notice cancellations due to staff shortages caused by the coronavirus pandemic.
ScotRail implemented a temporary weekday timetable on Tuesday as the Omicron variant of Covid-19 has resulted in a "large number of absences".
More than 150 daily services have been cut, including on routes such as Glasgow to Edinburgh via Airdrie/Bathgate; Glasgow Central to Lanark; Edinburgh to North Berwick; and Edinburgh to Tweedbank.
Other examples include Southern not serving London Victoria until January 10, while CrossCountry has removed around 50 daily trains from its timetables until next week.
Demand for rail travel is at around 50 per cent of pre-pandemic levels.