Silverstone racetrack has asked David Cameron to prevent tens of millions of pounds of potentially "illegal" state aid being used for a new £280m circuit in Wales.
Developers behind the Circuit of Wales scheme in Ebbw Vale, Blaenau Gwent, are said to be asking the Welsh and UK governments to commit up to £50m.
Silverstone has written to the prime minister to intervene.
Planning issues have delayed the start of work at the site.
Heads of the Valleys Development Company wants to create 6,000 jobs and bring 750,000 visitors a year to the area as part of its plans but doubts have been raised over the number of jobs claimed.
The development promises to transform one of Wales' most deprived communities.
Alongside the racing circuit, there are plans for hotels, a grandstand, a technology park and a solar park.
But those projects all rely on the racetrack going ahead.
The Circuit of Wales would host all motor racing events except Formula 1.
A spokesperson for Silverstone confirmed on Monday that its managing director Richard Phillips had written to Mr Cameron about funding for the Circuit of Wales.
The letter said: "An injection of funds by the Welsh and/or UK governments to the Circuit of Wales project would amount to a transfer of state resources, which gives Circuit of Wales an economic and selective advantage over other circuits. As such, it could amount to illegal state aid.
"There are a number of well established, privately funded circuits in the UK, including Wales, that feel that the British motor sport industry would be threatened by the addition of a government-funded circuit."
The Association of Motor Racing Circuit Owners, which represents 17 UK race tracks, said last summer the circuit would harm motorsport.
Developers have asked both the Welsh and UK governments for up to £50m in total towards the scheme, it was revealed earlier this month.
BBC Wales understands the Welsh government is considering investing £30m in the project.
The Welsh government told BBC Wales on Monday the Circuit of Wales had not asked it for money.
Prestigious event
Heads of the Valleys Development Company has also been asked to comment.
A key part of the racing circuit development involves securing the rights to host MotoGP - the motorbike racing equivalent of Formula 1 - which attracts global audiences of up to 300 million.
The company has said it aims to build the circuit in time to host the prestigious event in September 2015 but it is understood no deal has yet been signed.
It was hoped that building work could start on the site last December but there have been delays because of planning issues.
The circuit is being built on 332 hectares (820 acres) of common land so the company has to de-register it, find an equivalent amount of land elsewhere and re-register that as common land.
The Planning Inspectorate for Wales said the process could take almost a year to complete.
