The SNP’s Westminster leader on Wednesday demanded Boris Johnson take action and questioned the cost of an official sitting in both Westminster and Holyrood.
Mr Ross is already the MP for Moray, but is also running as an MSP candidate.
Calling for him to step down, Mr Blackford said: “We know that Tory leaders in Scotland have a habit of dodging democracy.
"Baroness Davidson is fleeing the House of Lords and the current Tory leader is too feart to stand in a constituency.
"Does the Prime Minister really have confidence in a Scottish Tory leader who doesn’t even have the courage to put himself before the voters in a Scottish constituency?
“The Scottish Tory leader is also seeking a place in the Scottish Parliament, but is refusing to step down as an MP.
"So as his boss, will the Prime Minister order the member for Moray to resign his seat, avoid a dual mandate and save the taxpayer £175,000, or are dual mandates one more Tory policy where they think greed is good?”
Responding, Mr Johnson insisted Mr Ross was doing an “excellent job”, but also referred to him as “The Member for Moray and Ross”.
He said: “[Mr Ross] is doing an excellent job of holding the SNP to account for their manifold failings not least on education, failing to deliver on crime, failing in my view to deliver for the people of Scotland, so caught up as they are in their desire for independence and another referendum for separation.
“[Ian Blackford] represents a party that’s so devoid of imagination that it can’t come up with any workable solutions to help the people of Scotland improve their education, improve the fight against crime, cut taxes in Scotland where they’re the highest in the whole of the UK.
“All they can talk about is a referendum to break up the UK … it’s twice he hasn’t mentioned it. Maybe he’s getting nervous of singing that particular song.”