The Scottish government has raised concerns over BT's offer to deliver universal high-speed broadband to all areas of the UK, as an alternative to regulation.
Ministers have promised to implement a new broadband Universal Service Obligation (USO) that ensures everyone in Britain has a legal right to request minimum speeds of 10Mbps by 2020.
According to the government, this is the speed that will meet the typical needs of a family that wants to browse the web, stream films and carry out video conferencing at the same time.
However, BT's offer would mean many premises would receive speeds substantially faster than 10Mbps, thereby rendering the planned USO unnecessary.
The Scottish government believes the plan may jeopardise its R100 programme - an effort to deliver superfast broadband to all properties in Scotland by 2021.
In a letter to Culture Secretary Karen Bradley, Rural Economy Secretary Fergus Ewing said: "We have engaged extensively with potential suppliers in recent months in order to stimulate competition through the forthcoming R100 procurement process.
"Indications from the market have been very positive and have shaped our procurement strategy."
However, Mr Ewing said the emerging USO proposal "risks undermining that engagement", as it suggests it will not be commercially viable for any provider other than BT to deliver in so-called white areas - places where no infrastructure currently exists.
"What has emerged as a result risks entrenching, even extending, BT's monopoly position in rural areas and could deter alternative suppliers from bidding for R100 contracts," he warned.
Mr Ewing said this would be a "hugely negative outcome" and would "undermine and frustrate the Scottish government’s digital ambitions".
He added that a working group should be set up to consider the "substance and implications" of BT's proposal.
The UK government will make a final decision on the BT plan following a consultation on the proposed USO.