Airline pilots are to become the first group to refuse to take part in the national identity scheme when compulsory trials start at Manchester and London City airports this autumn.

The British Airline Pilots' Association (Balpa ), which represents more than 80% of commercial airline pilots, is to mount a legal challenge to Home Office plans to use "critical" airside workers as the first compulsory "guinea pigs" for the scheme.

MPs are shortly to be asked to approve the powers to compel the pilots and other airside workers at the two airports to register for the national ID card scheme as part of their "pre-employment" checks. The £30 fee is to be waived as an incentive for them to sign up.

The pilots' union has protested to ministers that the £18m scheme cannot be regarded as voluntary when they are being told they will not qualify for an "airside pass" without them: "ID cards will have absolutely no value as far as security is concerned. This is nothing other than coercion and promises that ID cards would be voluntary have been broken," Jim McAuslan, Balpa general secretary, has told ministers. "We will resist."

These behind the scenes preparations and the recent signing of two 10-year contracts worth £650m to get the ID cards programme under way undermine recent speculation that the cabinet is considering axing the scheme as part of the general Whitehall spending squeeze. The speculation took off when a suggestion by David Blunkett, the former home secretary, that the ID card programme should be repackaged as a biometric passport scheme to reassure the public was misintepreted as him turning against the idea.

But the details of the two contracts awarded in the last few weeks show just how far the ID cards scheme has become embedded in the introduction of "biometric" passports. For 80% of British citizens their identity card will be their passport.

The Home Office describes the two contracts as "bringing the largescale deployment of ID cards a step closer". The first contract, worth £385m and awarded to a US computer company, CSC, will cover processing applications for passports and ID cards and dealing with any subsequent changes in personal details . The second contract, awarded to IBM, and worth £265m, is to build and run the database that will store the digital fingerprints and facial images for the ID scheme and the new generation of passports.

The decision to combine what the Home Office calls the core elements of the ID cards programme and the modernisation of the passports means it will be difficult for any incoming government after the general election to cancel the ID scheme separately.

Two further contracts will be awarded this year for the design and production of identity cards and the next generation of passports to be introduced from 2011.