Chiefs of the United States air traffic controllers union say they fear being continually squeezed by political conflict in their country.

The National Air Traffic Controllers Association leaders - who have been in New Zealand to thank their Kiwi colleagues for support during a 35-day government shutdown - say it was ''painful'' to see the system come apart.

A political row over border security funding led to the shutting down of a quarter of the US government earlier this year during which air traffic controllers who turned up to work weren't paid.

''There were statements like this could go on