MPs from Britain's opposition Labour Party were on Tuesday voting on a motion of no confidence against leader Jeremy Corbyn.
The secret ballot comes after Corbyn told supporters at a rally outside Parliament to not "let those people who wish us ill to divide us".
Shadow Justice Minister Andy Slaughter was the latest to leave his post, after a series of shadow cabinet departures since Sunday.
Shadow chancellor John McDonnell, however, said Corbyn was "not going anywhere".
He accused Corbyn's opponents of trying to "subvert democracy", and said the party leader would stand in any election if a challenger came forward.
The no-confidence vote is not binding.
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Corbyn faced calls to resign at a meeting in the House of Commons on Monday after more than 20 members of his shadow cabinet and a like number of junior ministers walked out, questioning his performance during the European Union (EU) referendum and ability to lead the party.
Margaret Hodge, the Labour MP who tabled the no confidence motion, said the Parliament Labour Party meeting had been "extraordinary".
"I couldn't believe the strength of feeling, the overwhelming rejection of Jeremy as our leader, and the pleading with him that he should consider his position and go with dignity," she said.
Corbyn's deputy Tom Watson told him he had "no authority" among MPs and faced the prospect of a leadership challenge.
Several Labour MPs have cited the possibility of a general election in the next six months, following on from the election of a new Conservative leader, as the reason why Corbyn must now consider his position.