Employees of Tower Hamlets Council were warned they may lose their jobs if they did not each illegally obtain 100 votes for Mayor Lutfur Rahman, according to court documents seen by BBC London.
Mayor Rahman and his party face claims of corrupt practices and exerting undue spiritual influence on voters.
A file obtained by the BBC now provides a raft of detail on the allegations Mr Rahman faces in court next month.
The mayor and his party Tower Hamlets First deny any wrongdoing.
The evidence will be heard over several weeks at the High Court by Richard Mawrey QC. He has the power to order a recount or ban the mayor from public office for up to five years.
Part of the Statement of Case, collated by the members of the public who brought the legal action, details an array of alleged misdeeds in the run-up to the election last May, when he was re-elected as mayor.
It claims that in April last year, 30 council employees were asked to a meeting at a Bangladeshi restaurant.
The document continues: "During the meeting both council managers and agents of the First Respondent [Mayor Rahman] instructed each of those attending to obtain 100 votes each for the First Respondent; and informed them that, if they did not do so, they may lose their jobs.
"It was made clear that these votes should be obtained by illegal means, including through postal voting fraud."
The petitioners allege that at another restaurant meeting in the period: "The First Respondent attended together with all or almost all the Tower Hamlets First candidates for the Council elections and some activists.
"The First Respondent told all assembled activists that they must fill up to 250 postal vote application forms each.
'Make Lutfur victorious'
"Each of the persons at the meeting was then given a bundle of 250 postal vote application forms."
A spokesman for Mr Rahman denied either meeting ever happened.
The documents also claim Mr Rahman and his party tried to exert undue spiritual influence over voters, which is illegal.
They state that a letter was published by a newspaper in Bengali with a circulation in the borough of about 20,000 entitled "Be United Against Injustice; Make Lutfur Rahman Victorious".
This was signed by 101 leaders of the Islamic community in the borough, including chairmen of Mosques and the head teachers of religious schools.
The petitioners allege the effect was to indicate that a vote against Mayor Rahman would be un-Islamic and sinful.
They claim Mr Rahman corruptly attempted to influence these religious leaders by giving them grants of public money ranging from £8,000 to £25,000, alleging that a total of £278,000 was given out in this way.
A spokesman for the mayor responded: "At no point did religious authority figures use spiritual coercion to procure votes. We believe such claims to be entirely spurious.
"Unless we are now in the business of disenfranchising the Muslim community, local leaders have a right to canvass for their preferred candidate."
There are also claims that during the count corrupt council officers deliberately miscounted votes.
The documents state: "In one instance a bundle of ballot papers purportedly containing only votes cast for the First Respondent was assembled by corrupt members of the counting staff and actually consisted mostly of votes for other candidates, with only the top few ballot papers containing votes for the First Respondent."
'Free and fair'
A spokesman for the mayor said: "All these allegations are characterised by an utter lack of substantial evidence.
"The police and Electoral Commission have already investigated and found nothing of merit, as has been the case when similar allegations have been made in the past by politicians.
"It is a shame that some elements of the local political establishment cannot cope with losing a free and fair election."
Tower Hamlets Council has made no comment.
Mr Rahman was previously Labour leader in the borough, before leaving during a split within the local party. He received 43.38% of first preference votes in May's election.
Numerous functions of the council have since been taken over by government commissioners after a report found numerous financial failings and what Communities Secretary Eric Pickles called a "culture of cronyism" within the authority.