The Chancellor faces a rebellion over Air Passenger Duty devolution that Conservative MPs warn will harm regional airports in England.
A group of 30 Tory MPs, led by former defence secretary Liam Fox, has written to George Osborne about a plan to devolve APD to Wales.
They fear airports in Wales would cut their rates to poach business from rivals in England.
The boss of Bristol airport warned last month that the economy in the southwest would lose £843 million and more than 1,500 jobs if APD were to be devolved to the Welsh government, which is likely to axe it altogether.
The Scottish parliament has already committed to cutting APD rates in half as part of a longer-term plan to abolish the air tax.
Bristol airport chief executive Robert Sinclair has voiced fears that the abolition of APD in Wales, which could be approved in Wednesday’s budget, would result in his airport losing a quarter of its passengers.
According to the Times, the letter to Osborne says: “Devolution of APD to Wales would create a taxpayer-funded incentive for airlines to relocate to Cardiff airport. Taking passengers and jobs with them.
“Ruling [it] out would ensure fair competition between airports, safeguard jobs and support growth.”
Cardiff airport is owned by the Welsh government which is pressing for devolution of APD.
A Treasury spokesman said it was considering how to protect English airports from any potential effects.
The Treasury previously confirmed that the government is considering devolving APD to Wales in parallel to a review of options to support regional airports from the impact of APD devolution.