Orient supporters attending this weekend's final league game at MK Dons have been asked to retain their tickets in case the club need to prioritise sales for the away leg of the play-off semi-final.
If the number of tickets allocated to Orient for the away leg does not exceed the number of season ticket holders, the club will introduce a secondary method of prioritising sales.
Orient are fourth in the table but could finish third if they manage to win at MK Dons and Preston fail to beat Crewe.
If the O's finish third, they will play away to Peterborough United on Saturday, May 10 at 12.15pm with the return match coming the following Tuesday at 7.45pm.
But should Orient finish either fourth or fifth then the legs would be held on Saturday, May 10 at 5.15pm and the following Thursday night at 7.45pm.
The fourth placed side will have the advantage of playing the second game at home with the winners advancing to the final at Wembley on Sunday, May 25.