Boris Johnson is facing a growing rebellion from his own MPs on Monday over breaking his manifesto and legal commitment to spend 0.7 per cent of gross national income on overseas development aid.
An amendment brought by former international development secretary Andrew Mitchell will go to the Commons and has been backed by around 30 Tory MPs, including former Prime Minister Theresa May.
Now the SNP's Westminster deputy leader Kirsten Oswald has urged Mr Ross to speak out against the plans.
She said: "The Tory government's cuts to the aid budget in the middle of a global pandemic is callous to the core, punishing some of the world's poorest and most vulnerable as they face a disproportionate hit from the Covid crisis.
"It tells you all you need to know about this Tory government's toxic priorities that as our international partners recognise the challenges and strengthen their aid spending as we prepare for key global summits, the UK is instead pulling up the drawbridge by cutting support and isolating itself further.
“With cross-party efforts building, Douglas Ross and the Scottish Tory MPs must end their deafening and shameful silence, and make clear that they will back the amendment to reverse the aid budget cuts.
"This is a test of leadership for Douglas Ross. Will he finally find a backbone and vote to restore the aid budget and to protect lives? Or will he and his colleagues simply cower and fall into line behind Boris Johnson as they have done time and time again?"
Other MPs backing the amendment include former Brexit secretary David Davis, former ministers Johnny Mercer, Damian Green and Tim Loughton, and the former Welsh secretary Stephen Crabb.
Mr Mitchell explained: “More and more of my colleagues in the House of Commons are supporting this move to stand by our manifesto promise. With our economy returning to growth, there is no justification for balancing the books on the backs of the world’s poor.
“With G7 leaders coming to Britain next week, there is an opportunity for us to reclaim our rightful place on the global stage.
"Britain’s national interest is not being served by the devastating impact these cuts are already having on the ground and the unnecessary loss of hundreds of thousands of innocent lives. We urge the government to think again.”
The vote is a major embarrassment for the UK Government coming just before the UK hosts the G7 summit where one of the key themes will be helping poorer countries.
A Scottish Tory spokesman said: “The United Kingdom has been and always will be open and outward-looking, leading in solving the world's toughest problems and striving to be a force for good in the world, whether it is leading the fight against Ebola and malaria or helping millions of children across the globe to gain a good education.
“The UK Government is one of the most generous aid donors in the G7, and will be spending more than £10 billion in 2021 on climate change and biodiversity, global health security, responding to humanitarian crises, girls’ education, science and technology, resolving conflicts and promoting trade.”