Around 600 people are on the verge of missing out on attending Gallipoli centenary commemorations.

Successful applicants for 300 double passes have until tomorrow to confirm their places - if they don't the tickets will be reallocated in another ballot.

Veterans' Affairs Minister Craig Foss says there's been extensive correspondence with the applicants and he doesn't know why they haven't responded.

"I'm not sure. To be fair 600 people already have gone down that route of confirming, so the other 300, it's only fair on them and themselves and others on the waiting list to make their decisions so we can have confirmation and clarity pretty quickly."