Donegal and Mayo fans have gone to war on the counties' biggest mountains
Fans have invaded each other's territory to plant "foreign" flags behind enemy lines ahead of the All-Ireland final.
Last weekend Donegal TD Joe McHugh posed for pictures on top of Croagh Patrick in Co Mayo, proudly displaying a Donegal flag.
The Fine Gael politician said he wanted to remind his boss Enda Kenny that there would be no loyalty to him this Sunday.
And yesterday three Mayo fans retaliated by climbing Mount Errigal in Co Donegal and proudly putting their colours on the peak.
The group were so delighted with their work, they even posted a video on YouTube.
Mr McHugh welcomed the Mayo fans' move.
"I'm delighted to see that the All-Ireland final is generating much-needed tourism to Co Donegal," he laughed.
The Fine Gael man said that when he climbed Croagh Patrick, he couldn't resist the chance to plant the flag.
"There was a Mayo flag there. Out of respect I didn't remove it, but let's just say the Donegal flag was flying much higher than it when I left," he added.