More than 500 trains are due to be halted over much of the Scottish network in an increasingly bitter row over conductors being paid less than drivers for working on days off.
The scale of the disruption is believed to be because ScotRail has been unable to train managers to step in to run trains because of Covid restrictions, but the operator declined to confirm this.
ScotRail said some 510 of the normal 1,090 Sunday services would not run – or 47 per cent.
All lines where conductors rather than drivers control train doors will be hit – which means virtually every route away from the west of Scotland.
Aberdeen – Glasgow/Edinburgh
Aberdeen – Inverurie/Inverness
Aberdeen – Perth/Dundee
Edinburgh – Inverness/Aberdeen
Edinburgh – Inverkeithing/Glenrothes/Kirkcaldy/Perth/Dundee
Edinburgh – Stirling/Dunblane
Edinburgh – Tweedbank
Edinburgh – North Berwick
Edinburgh – Glasgow Central via Shotts
Glasgow – Edinburgh via Falkirk High
Glasgow – Anniesland
Glasgow – Stirling/Alloa/Dunblane/Perth/Dundee
Glasgow – Inverness/Aberdeen
Glasgow – Cumbernauld
Glasgow – Alloa
Glasgow – Barrhead/Kilmarnock/Dumfries/Carlisle
Glasgow – Stranraer
Glasgow – Crainlarich/Oban/Fort William/Mallaig
Inverness – Aberdeen/Edinburgh/Glasgow
Inverness – Kyle of Lochalsh/Wick
The action is due to continue every Sunday until May 2.
Further walkouts are threatened if the dispute is not resolved.
The disruption could also be widened if ticket examiners, who work on trains in the Glasgow area, vote for action next month.
The strikes have been called by the Rail, Maritime and Transport union (RMT), which has accused ScotRail of “inflammatory and condescending” remarks by suggesting the walkouts were targeting key workers.
It accused the company of trying to emotionally blackmail conductors, who it said were key workers too.
RMT general secretary Mick Cash has told them: “All through this awful pandemic, you have been on the front line, putting your own and your families’ and friends’ health at risk to ensure services are run so other key workers can get to work.
"It is unbelievably insulting to you and your colleagues and shows how out of touch this company is.
“It's frankly disgusting that rather than recognising the issues at the heart of this dispute, the company have resorted to disgraceful mud slinging.”
ScotRail said the action “will have a significant impact on people who need to travel, including NHS workers delivering a critical service during the pandemic”.
It said limited buses would run for key workers to University Hospital Hairmyres in East Kilbride, Queen Margaret Hospital in Dunfermline and Victoria Hospital in Kirkcaldy.
The operator said the strike ballot was held despite all staff jobs being protected by emergency Scottish Government support, with no one furloughed or having their basic wages or terms and conditions reduced.
ScotRail head of conductors Graham Ralston said: “The strike is wrong during a global pandemic and will have a significant impact on those who need to make essential journeys.
“We will do everything we can to minimise the consequences of this action, but key workers will be adversely affected.
"Inevitably, many will have to find alternative and much less convenient ways to get to work to perform their life-saving duties.”