Australia's Deputy Prime Minister was under mounting pressure to resign yesterday as his party's leader over revelations of a relationship with a former staffer.

Newspapers revealed last week that Barnaby Joyce and his former media adviser are expecting a baby together, and the scandal has angered many within Joyce's conservative, rural-based Nationals party. As leader of the junior party in the governing coalition, Joyce is both the Deputy Prime Minister and acting Prime Minister when the Prime Minister, Malcolm Turnbull, is overseas.

Nationals lawmaker Ken O'Dowd said he expected a party delegation would confront Joyce soon to consider his position. "The party will probably talk to him and discuss the future of Barnaby and the future of the ... party," O'Dowd told reporters. "He'll probably need the advice and someone needs to tell him where the party stands at this stage."

If Joyce resigns, "we would find a good leader, I feel sure about that", O'Dowd added, without naming a potential replacement.

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Agriculture Minister David Littleproud, a senior Nationals lawmaker, said most of the party still supported Joyce's leadership.

"If people believe that Barnaby Joyce has broken the law, then lay charges. Otherwise leave him and his family alone," Littleproud told ABC.

Nationals president Larry Anthony, the party's most senior bureaucrat and a former legislator, arrived at Parliament House yesterday telling reporters he was helping lawmakers deal with "a very difficult time".

Joyce, 50, revealed in December that he had separated from his wife of 24 years who is the mother of his four daughters. But he has kept tight-lipped about his relationship with Vikki Campion, 33, describing it as private. The reports have said they are expecting a son in April.

He has denied allegations that he had breached guidelines surrounding giving jobs to ministers' partners when Campion was given a promotion last year to leave his office for another government job. He has also denied published allegations that he sexually harassed women in a Canberra bar while drunk in 2011.

Joyce is to become Australia's acting Prime Minister next week when Turnbull travels to the United States. Foreign Minister Julie Bishop said yesterday that she would step in as acting prime minister if Joyce was not available.

Meanwhile, a petition to demand removal of Joyce from his New England seat has received more than 7000 votes in five days.