The Liberals and the Nationals look set to go head-to-head in a Senate showdown, with the coalition partners at odds over the NSW ticket for the next election.
Deputy Prime Minister Michael McCormack signalled the Nationals could run a separate ticket to the Liberals after his predecessor Barnaby Joyce and party elder John Williams supported the idea.
"I'm not ruling anything in or anything out. The fact is we've preselected four outstanding candidates," Mr McCormack told reporters in Canberra on Thursday.
Under an existing agreement, the NSW Nationals will get third spot on a joint coalition ticket, but party members consider this to be unwinnable and want second place.
The Nationals have preselected Conargo businesswoman Perin Davey to top their NSW Senate ticket.
Mr Joyce on Wednesday said the Nationals should "absolutely" run a separate campaign if they were denied the second position on a joint coalition ticket.
The Nationals did not run a candidate in the Wagga Wagga state by-election, which was won by an independent candidate in a disaster for the Liberals.