Leadership strains within the 20-strong Nationals party room have intensified with the heir-apparent Barnaby Joyce accused of trying to hurry current leader Warren Truss out the door.

At issue is the highest rank attainable by a Nationals MP, that of Deputy Prime Minister.

It comes as Bill Shorten heads into the Nationals heartland on Saturday to hammer the message that the rural party is split over its leadership, beholden to the Liberals, and can no longer be regarded as the natural representatives of rural and regional Australia.

While Mr Joyce has denied disloyalty, angry pro-Truss Nationals say the man Tony Abbott had described as Australia's best "retail politician" seems to have concluded that his chances of securing the leadership are fading unless the change-over happens soon, meaning before the end of the year.