Every full node peer on the network verifies every block they receive before relaying them and adding them to the blockchain. If 99% of the miners are publishing blocks that have a larger reward than the peers allow, those blocks will be relayed among those miners, but will never make it to the users or the miners that don't accept that rule. They will essentially have created their own cryptocurrency separate from bitcoin (though they may try to call it bitcoin as well).
The 99% of the miners would devote 2% of their mining power to ensuring that no transactions ever survived in the longest chain in the fork they consider illegitimate. 51% of the mining, if sufficiently organized, can enforce whatever rules it wants. They get to decide what chain is usable.