Once a bill is approved by one house, it is sent to the other which may pass, reject, or amend it. For the bill to become law, both houses must agree to identical versions of the bill. If the second house amends the bill, then the differences between the two versions must be reconciled in a conference committee, an "ad hoc" committee that includes both senators and representatives sometimes by using a "reconciliation process" to limit budget bills. Both houses use a budget enforcement mechanism informally known as "pay-as-you-go" or "paygo" which discourages members from considering acts that increase budget deficits. If both houses agree to the version reported by the conference committee, the bill passes, otherwise it fails.