Former Home Office Minister Ann Widdecombe is slicing up her frequent flyer card and sending it to British Airways if the company refuses to overturn a "loopy" policy, which bans a Christian employee from displaying her cross necklace.
The Tory MP, a practising Catholic, has set a deadline of this evening and has urged others to consider boycotting the company.
If BA does not reverse its widely-criticised uniform code, she will cut up her card and avoid using the airline until the decision is reversed.
Nadia Eweida, 55, from Twickenham, West London, who works at Heathrow, said 200 of her work colleagues have signed a petition backing her, adding: "Nothing is impossible with God".
Miss Eweida claims she was effectively "forced" to take unpaid leave after refusing to remove the cross, which is about the size of a five pence piece. She plans to sue the airline.
She is supported by the Transport and General Workers' Union and says she has been "overwhelmed" by support and "very grateful".
Miss Widdecombe claimed the decision was "religious discrimination".
She also backed calls for a day of solidarity this Friday - where Christians across the UK should "wear the biggest crosses they have".
She told the BBC's Heaven and Earth programme: "As far as I'm concerned, this is religious discrimination and I don't think Christians have to take it."
She added: "If this decision isn't reversed by tomorrow evening - I'm going to cut up my frequent flyer card - and send it to BA so they know why I've done it. And in future - until the decision is reversed, I shall not use BA."
