Special Dues Systems:

BARD -
    Bard requires that you've explored at least 6% for level 16,
    8% for level 17, 12% for level 18, etc, up to 20% for level 20.
    Bard also requires you to complete level quests.  6 are required
    for level 16, 8 for level 17, 10 for level 18, etc, up to 14 for
    level 20.  Exploration is not lost over reincarnation.
    These dues are not spent when advancing.

FALLEN -
    Fallen require that you've built up a worthy Fellblade.
    Only points spent on the Fellblade count towards this.
    2k power points are required for level 16, 6k for 17, 
    10k for 18, up to 18k for level 20.
    These dues are not spent when advancing.

NECROMANCER -
    Necromancers earn dues by training and advancing their
    undead creations. The dues earned are based on the tier 
    to which it is advanced and which skills they train. They
    also gain dues from using the spells siphon life and
    vestige recovery.

PALADIN -
    Paladin requires that you've built up a worthy Shield.
    Only points spent on the shield count towards this.
    2k honor is required for level 16, 6k for 17,
    10k for 18, up to 18k for level 20.
    These dues are not spent when advancing.

See also: HELP DUES COSTS, HELP GUILD DUES