In a leaked email, she is reported to have said she agreed to support Mr Ross on the understanding he leads a “Boris backing, Brexit positive, anti nat party”.
Mrs Ballantyne, who was beaten in the last leadership race by Jackson Carlaw, had written to Tory colleagues calling for and end to “cronyism” within the party.
In the email, which was reported on in the Daily Record, she wrote: “I have spent all morning on the phone with regards to the leadership contest – I can’t obviously give you all the detail but I have spoken with key people (not MSPs!) about what is happening and I am now content to back Douglas.
“This is on the understanding that we will be a centre right Conservative, Boris backing, Brexit positive, anti nat party.
“And that we will see reform of the cronyism starting with the candidates board not being made up of candidates!
“I know this is potentially difficult for some of you but I think right now this is the right decision as we are now incredibly short of time.
“I have told them that if the party doesn’t reform I will design [sic] so I will back Douglas on the basis of change and judge his performance accordingly.”
Her stance has come under fire from the SNP.
Chrisine Grahame, SNP MSP for Midlothian South, Tweeddale and Lauderdale, said: “This leaked message confirms that Douglas Ross is Boris Johnson’s man in Scotland and will rubber-stamp every damaging decision from Downing Street regardless of the harm it could do.
“People here didn’t vote for Brexit, or the Tories, and Michelle Ballantyne’s comments couldn’t be further out of step with public opinion here.
“Douglas Ross might be promising a party which doesn’t take its orders from Westminster – but no one is buying it.
“Even under a change in leadership, the Tories will be the same old party – obsessed with a Brexit Scotland didn’t vote for, no matter the cost to jobs and livelihoods, and happy to line up beside Boris Johnson in any election.
“Time and time again, the Tories have proved themselves no different to their colleagues at Westminster – they are completely out of touch, and utterly incapable of standing up for the interests of Scotland.”
Mrs Ballantyne, who also angered some of her colleagues by criticising Mr Carlaw’s performance as leader hours after his resignation, told The Southern: “There is nothing new in my comments, I called for change in January.”
“I am not at all surprised by the SNPs reaction, but they should perhaps focus their attention closer to home and ask whether they are happy with the way their own party is run as I can see huge amounts of cronyism in the SNP – let’s start with the First Minister being married to the chairman of the party [Nicola Surgeon’s husband Peter Murrell, is the chief executive officer of the SNP], or the manner in which they have tried to control the selection for Edinburgh Central.”
“Instead of using leaked private messages to try and distract from their own problems, maybe Christine Grahame should call for reform of the SNP or offer her resignation – but then that would require the commitment to independence not to transcend everything.”
However, Mrs Ballantyne’s two Conservative colleagues in the Borders are fully behind Mr Ross’s bid to become the leader of the party in Scotland.
John Lamont, MP for Berwickshire, Roxburgh and Selkirk, is indeed his campaign manager.
He said: “I am absolutely delighted that my friend and colleague Douglas Ross has put his name forward to be the next leader of the Scottish Conservative and Unionist party.
“During his time in the Scottish Parliament and at Westminster, he has demonstrated that he is a formidable political figure.
“Not only has he shown himself to be a powerful voice for Scotland, but also that he can provide the robust leadership we need to unite pro-UK voters across Scotland.
“We need to demonstrate what we all gain from Scotland being at the heart of the United Kingdom. I believe Douglas is best placed to deliver this important message.”
And Rachael Hamilton MSP for Ettrick, Roxburgh and Berwickshire, said: “I’ve known Douglas for many years and he has what it takes to be a great leader.
“He will take the fight to the SNP and win, he has already done so twice in his own constituency of Moray.
“With Douglas Ross at the helm, we can build a positive and forward looking vision for Scotland at the heart of our United Kingdom.
“He has vowed to put jobs, education and the NHS at the top of his list, and show how we are being hoodwinked by this SNP Scottish Government.
“Douglas is determined for our party to succeed and I know with his leadership, we will show Scotland that there is an alternative to the grudge and grievance politics of the narrow-minded SNP.”
Mr Ross, the MP for Moray, looks as if he will be crowned party leader later this week as to date, no-one else is challenging him.