Abusive Labour supporters will be stripped of their leadership contest vote, the party's general secretary has said.
Iain McNicol warned there is "simply too much" abuse, intimidation and shouting down of members taking place online and at meetings.
He recognised condemnation of such "appalling behaviour" from leader Jeremy Corbyn and his challenger Owen Smith, among others, but added such comments are "meaningless unless they are backed up by action".
Members responsible for abuse will also be investigated and could be suspended while this work takes place, Mr McNicol added.
His warning came as Mr Smith said Mr Corbyn and shadow chancellor John McDonnell's aides breached parliamentary privilege if they entered a Labour MP's House of Commons office without permission.
Mr Smith described Seema Malhotra's claim as an "internal little spat" but said staffers should not have entered the former shadow minister's office without her permission.
The leadership contest is set to intensify throughout the summer, with the level of interest in the outcome being demonstrated by the huge number of people who paid the £25 required to become registered members with a vote in the contest.
More than 183,000 people paid the fee during the 48-hour window for such applications last week.
Outlining the behaviour expected of members, Mr McNicol said: "For a fair debate to take place, people must be able to air their views in an atmosphere of respect. They shouldn't be shouted down, they shouldn't be intimidated and they shouldn't be abused, either in meetings or online.
"Put plainly, there is simply too much of it taking place and it needs to stop."
Mr McNicol also said the leadership election must be conducted in a way that gives "confidence in our ability to build a better Britain" to potential Labour voters.
He said: "The NEC has already taken the difficult decision to suspend most party meetings while the leadership election is ongoing.
"And over the coming days and weeks the party will be taking further action to protect our members and to identify those responsible for this appalling behaviour.
"I want to be clear, if you are a member and you engage in abusive behaviour towards other members, it will be investigated and you could be suspended while that investigation is carried out.
"If you are a registered supporter or affiliated supporter and you engage in abusive behaviour, you will not get a vote in this leadership election."
Ms Malhotra, a former shadow Treasury minister, has lodged a formal complaint with Speaker John Bercow, claiming staff working for Mr Corbyn and Mr McDonnell entered her office in a serious breach of parliamentary privilege.
But Mr McDonnell said the office manager concerned had simply been checking whether Ms Malhotra had moved out of the office after quitting the front bench last month in protest at Mr Corbyn's leadership.
And a spokesman for Mr Corbyn played down the incident and said claims of intimidation are "untrue".
Commenting on the party's latest row, Mr Smith told BBC Radio London: "Obviously people shouldn't be going into MPs' offices, obviously that's abuse of parliamentary privilege.
"But I don't know enough about the details."
Elsewhere, Labour's shadow Lords leader Baroness Smith of Basildon revealed she would support Mr Smith in his battle with Mr Corbyn for the leadership.
The peer criticised Mr Corbyn for claiming credit for Government U-turns on tax credits, trade union reforms and housing without acknowledging colleagues.
The shadow cabinet member's comments came after Mr Corbyn released an advertisement urging members to back him for the leadership which trumpeted the victories.