Counter target spell unless its controller pays. If that player doesn't, they tap all lands with mana abilities they control and lose all unspent mana.
10/4/2004 Does not increase the mana cost of the spell. It just requires a separate expenditure in order for it to succeed.
10/4/2004 When this spell resolves, you either pay X mana or let your lands become tapped. The lands that become tapped are not “tapped for mana”. If you choose to pay, you may pay the X mana using whatever mana abilities you want to use.
3/1/2010 Only lands that actually have mana abilities will get tapped. This includes basic lands and lands with mana abilities printed on them, as well as lands which have been granted a mana ability by some effect.