Witnesses in the court case into allegedly corrupt electoral practices in Tower Hamlets have been intimidated, petitioners claim.
Mayor Lutfur Rahman and his party, Tower Hamlets First, face claims of bribery, corrupt practices and exerting undue spiritual influence over voters.
Members of the public who brought the case now say 11 of their witnesses have been harassed for their involvement.
The mayor said he was "astonished" by the claims.
The deadline for all parties involved to respond to initial evidence and statements expired at 18:00 GMT.
The court case - which does not yet have a start date - will hear:
- Dozens of allegations of postal ballot fraud and of people pretending to be registered voters.
- Claims that some votes for Labour were not counted properly by Tower Hamlets staff.
- Alleged "treating" of voters to secure their support, which is forbidden under election law.
Some unnamed voters claim they were told at polling stations by the mayor's supporters: ''You must vote for Lutfur otherwise you are not a good Muslim.''
BBC London has now been told that 11 potential witnesses have come under pressure for their involvement in the case.
The daughter of one witness, who was said to have provided a statement about "treating", was allegedly threatened in the street.
One man who complained to police that his and his wife's postal votes were taken from him has allegedly been approached several times by strangers in the street asking him why he is "attacking the mayor".
Azmal Hussain, one of those who has brought the petition, also says he has been intimidated and his vehicle vandalised.
He told BBC London: "I am very afraid to go out alone. If I forget my telephone my friends call me 10 times - 'are you ok'?
"Even my friends are afraid."
Mr Hussain, who runs a Brick Lane restaurant, said on Wednesday he was accused of not being a "real Muslim" in the mosque because of his involvement with the case.
The police have advised him on taking precautions.
The Met said it had received information from third parties alleging possible witness intimidation.
A spokeswoman said they had received no specific evidence of any offences at this time and no allegations had been reported by alleged victims.
They urged anyone with concerns to contact them.
The spokeswoman said they were aware of the allegation of ballot paper theft made in May, but that the individual was now refusing to answer calls from the police.
She said officers asked the man who made an allegation of 'treating' whether his daughters wanted to report any crime, but they subsequently declined.
The BBC understands that at least one witness has now given a statement to the mayor's legal team which contradicts an earlier statement given to the petitioners.
The petitioners have said they do not allege or imply that the reported intimidation has been orchestrated by any known individuals.
Mayor Rahman said: "I'm astonished by these claims. I have not seen any evidence of witness intimidation but were I to see any I would report it to the police.
"I have seen or heard nothing to suggest there is any truth to these allegations."
The mayor denies all allegations of electoral malpractice.
On Monday ballot papers that are alleged to have been tampered with or miscounted are due to be rechecked by court staff.
Court officers are due to spend four days on the operation.
Since the disputed election, the ballot papers have been kept by Tower Hamlets Council - a situation the petitioners say is akin to allowing the accused in a criminal case to keep crucial evidence at his home.
John Williams, Tower Hamlets returning officer, said: "There is an ongoing court hearing and the correct method for ensuring allegations are examined is to place the evidence before the court or the police as appropriate."
During the court case Mr Williams will face allegations about his running of the election, including claims he allowed people to canvass for votes inside polling stations, accompanying voters into booths as they cast their vote and leaving campaign material in and around voting booths.
Mr Williams has previously said: "I totally reject the allegations made against my running of the May election."
The case has been brought by four Tower Hamlets voters, all of whom have political affiliations.
The trial will be presided over by Richard Mawrey QC. He has the power to order a recount or a scrutiny, which would involve scrutinising the signatures on the postal ballot papers.
He could also ban the mayor from public office for up to five years.