New Zealand's second- and third-largest political parties are teaming up to try and stop the dominant National Party from winning a fourth straight election.

The Labour Party and the Green Party announced Tuesday that they have signed an agreement to coordinate their efforts ahead of the 2017 general election. The parties said they would support each other's bills, give advance notice of major announcements, and investigate joint policies and campaigns.

The two left-leaning parties said they would remain independent entities and will agree to disagree on some issues.

The two parties have made little headway in the polls since the center-right National Party first took office in 2008. Polls indicate Prime Minister John Key remains relatively popular after eight years as New Zealand's leader.