Track on the Chase line – which connects Rugeley Trent Valley with Birmingham New Street via Walsall – will be "renewed" through the scheme.
Railway chiefs say the essential upgrades as part of Network Rail's commitment to get the railway in the best shape as possible amid coronavirus.
Work is already under way – having started on June 27 – and work will progress over this Sunday, July 11 and July 18, with parts of the railway closed.
Dave Penney, Network Rail’s Central route director, said: "These essential upgrades to the Chase line are part of Network Rail’s commitment to get the railway in the best possible shape as passengers return to the network after the coronavirus lockdown.
"The improvements will mean fewer delays caused by track related issues and the new rails will mean smoother journeys for passengers. I’d urge anyone planning to travel on Sundays over upcoming weeks to check before they travel for the latest information."
Parts of the railway line will be closed, with trains only running between Birmingham New Street and Walsall, and buses in use between Walsall and Rugeley Trent Valley.
Jonny Wiseman, customer experience director for West Midlands Railway, said: "We know our customers appreciate a smooth ride which is why it is important we allow Network Rail to access tracks to carry out these improvements.
"I thank our passengers on the Chase line for their patience while these works are carried out and I urge anyone needing to travel on affected Sundays to plan ahead."