Do you mean riders? https://secure.wikimedia.org/wikipedia/en/wiki/Rider_%28legi... The House actually has a "germanness rule" (which is not in the Constitution), so they generally avoid it as a matter of policy. But the Senate has no such rule. https://secure.wikimedia.org/wikipedia/en/wiki/Christmas_tre... So a bill which passes the House goes to the Senate, where riders are added. Then the modifications go back to the house, where it might be passed depending on whether they like the new additions or not.