Now, the owners of the Navajo Generating Station must decide whether they can agree to the changes.
The legislation extends the lease to 2044 and boosts yearly payments to the tribe from $3 million to $43 million. It also provides money for scholarships and gives the Navajo Nation a shot at partial ownership of the power plant near Page.
Lawmakers on Monday tacked on amendments to control fly ash, protect claims to water and name the federal government as a lessee.
A spokesman for the plant operator said Tuesday that the owners would be reviewing the changes.