Avanti West Coast services from London to Edinburgh Waverley and Glasgow Central are being delayed by up to ten minutes pending repairs between Symington and Thankerton in South Lanarkshire.
Network Rail said a machine which spreads ballast stones under the tracks had damaged the sleepers they rest on over a two-mile stretch on Sunday night.
This has forced northbound trains to slow to 20mph through the area as a precaution.
Repairs are scheduled for the May bank holiday weekend to coincide with other planned work on the line.
The official rail industry JourneyCheck travel information website stated: “Due to a speed restriction between Carlisle and Glasgow Central trains have to run at reduced speed on some lines towards Glasgow and Edinburgh.
"Train services running to and from these stations may be delayed by up to 10 minutes.
"Disruption is expected until 6am on Sunday May 2.
Network Rail said the damage had been caused by a “ballast regulator” machine near Thankerton.
Its spokesperson said: “Weekend engineering work resulted in damage to some sleepers on the northbound track and trains are running at a reduced speed until repairs are complete.
"We will repair the line as quickly as possible and the cause of the damage, due to an equipment failure, is being fully investigated.”
The incident happened a week after a ScotRail Inter7City train derailed at Dalwhinnie, which blocked the Inverness-Perth line for five days.