Some train services that serve Lydney and Chepstow would be affected by planned strikes next month.
Train drivers belonging to the RMT union have agreed to take industrial action on February 1 and February 3 in response to the cost of living crisis.
The dispute affects 14 rail companies – among them CrossCountry Trains whose Cardiff to Nottingham route includes stops at Lydney and Chepstow.
The strike action will also affect GWR which provides connecting services to London, the South West and Portsmouth.
Services operated by Transport for Wales between Cardiff and Gloucester will not be affected by the strike.
The decision to strike on February 1 coincides with a TUC day of action where several unions are coordinating their strikes during the cost-of-living crisis.
RMT general secretary Mick Lynch said: "Our negotiations will continue with the rail operators to create a package on jobs, conditions and pay that can be offered to our members."
The other affected companies are Chiltern Railways, Greater Anglia, LNER, East Midlands Railway, c2c, Northern Trains, South Eastern, South Western Railway, Transpennine Express, Avanti West Coast,West Midlands Trains and GTR, including Gatwick Express