A trade union leader has issued a new warning to Labour MPs not to stand in the way of Jeremy Corbyn's agenda for change.
Matt Wrack, general secretary of the Fire Brigades Union (FBU), said there was a clear mood among the party's grassroots members who swept Mr Corbyn to the leadership that they wanted MPs who supported his policies.
He said it would inevitably lead to a debate within the party around the issue of "who represents Labour in Parliament".
His comments will heighten fears among moderate Labour MPs that they could be targeted for de-selection by Mr Corbyn's supporters, despite the leader's insistence that he does not want to see MPs ousted.
However Mr Wrack - a long-time ally of Mr Corbyn whose union recently re-affiliated to Labour - said MPs could not expect to be selected at the age of 25 and then remain "for the next 40 years without having to have some dialogue and debate with the people who put them there".
"The election of Jeremy Corbyn reflected a mood among a whole layer of people for change in politics. You can't blame those people who got involved in that want to then want to see that through," he told the BBC Radio 4 Today programme.
"They also want representatives in Parliament who will see those sort of policies through so there is going to be a debate around issues like who represents Labour in Parliament.
"That is a matter for local Labour parties to determine who is going to be the Labour candidate in the 2020 election or in local elections or the other elections next May.
"But clearly there is a mood to ensure that the policies on which Jeremy Corbyn stood in defence of public services, in defence of workers' rights, in defence of people's living standards and so on are actually seen through."
His comments came as it emerged that a second Labour MP has received an apparent death threat after backing military action against Islamic State in Syria.
Simon Danzcuk was warned in a Facebook posting that the sender would cause him "some serious damage, probably resulting in your death".
The message was sent after the MP for Rochdale - an outspoken critic of Mr Corbyn - confirmed he was planning to back air strikes in Wednesday's Commons vote.
The disclosure comes after Bermondsey and Old Southwark MP Neil Coyle revealed he had been given police protection after receiving a death threat on Twitter when he voted for military action.
The message to Mr Danczuk described him as "f****** scum", adding: "I'm going to find you and do you some serious damage. Probably resulting in your death and do the country a massive favour."
The MP said he had reported the matter to the police.
"It's not acceptable in a civilised society for MPs to receive death threats, no matter how emotive the issue might be," he told the Manchester Evening News.