John,
From memory, don't those relays activate in a 20mT field? In other words, all your OPEN relays will CLOSE in that strong a field. Right?
Anyway, bet once you 'qualify' those relays to sit in a static field; your customer will admit that the field migh possibly change once in a while and you'll have to qualify for ramp up/ramp down too. and maybe overshoot, etc etc.
Is the field guarranteed to be somewhere? Like some orientation? A field that value just can't be omnidirectional. Therefore you can 'shadow' the field down by placing adjacent metal pieces made from standard transformer leaves. Can check, but they should handle that level of field AND suck the field over to themselves, providing a 'bypass' away from your relays, with that much lower field, you could then properly shield the relays in mumetal, or such, and really drop what the relay 'sees'.