MELBOURNE (REUTERS) - Australia's embattled deputy prime minister, under pressure over an extramarital affair, faced a call to step down as leader of his party on Thursday (Feb 22), the first such call from a member of the party, which is part of the ruling coalition.

Mr Barnaby Joyce who has campaigned on "family values" and who has been married for 24 years, refused to resign when it was made public he was expecting a child with his former staffer.

"He needs to step down as leader of the National Party, take a step back into the back bench for a time," Mr Andrew Broad, a member of parliament from Mr Joyce's National Party, told state-owned broadcaster the ABC.

The National Party is in a ruling coalition with Prime Minister Malcolm Turnbull's Liberal Party. The coalition holds a one-seat majority in parliament.

Mr Turnbull has called Mr Joyce's affair a "shocking error of judgment".

Mr Broad said he would take up the issue of Mr Joyce's leadership at a party meeting in the capital, Canberra, on Monday (Feb 26).

His call is the latest sign that support for Mr Joyce from within his rural-based party is eroding, amid concern disapproval of the affair could undermine support in state elections.

A state branch of the party withdrew its support for Mr Joyce this week because of the affair.

Two-thirds of voters want Mr Joyce to resign over the affair, according to the Australian newspaper's Newspoll.