Prime Minister Boris Johnson is expected to set out his decision later on the findings of an inquiry into the conduct of Home Secretary Priti Patel.
Sources familiar with the Cabinet Office report told the BBC it concluded Ms Patel broke rules on ministers' behaviour.
She has always strongly denied allegations of bullying.
Labour said the prime minister appeared to be involved in a "cover up" and called for the report to be published.
Shadow Home Secretary Nick Thomas-Symonds said: "If these revelations are correct, it is tantamount to condoning bullying, and in no other workplace would this be acceptable. It smacks of one rule for the government and one rule for everyone else."
Normally if a minister breaches the code they are expected to resign. But a number of Tory MPs have rallied round Ms Patel, describing her as a determined person doing a tough job.
Health Secretary Matt Hancock told the BBC she was an "excellent home secretary" who had "been nothing but courteous and kind in all the dealings I've had with her".
Mr Johnson has backed Ms Patel so far and there is little sign that will change.
The inquiry was launched after Home Office boss Sir Philip Rutnam resigned in February.
Sir Philip - who is suing for constructive dismissal - alleged staff felt that Ms Patel had "created fear".
Who is Priti Patel?
- Born in London to Gujarati parents who left Uganda in the 1960s, she was educated at a comprehensive girls' school in Watford before studying at Keele and Essex universities
- Worked at Conservative Central Office, but left to run the press office of the Eurosceptic Referendum Party from 1995 to 1997
- Had a career in public relations before becoming an MP at the 2010 election
- Leading figure in the Vote Leave campaign during the 2016 EU referendum
- Appointed international development secretary by Theresa May
- Resigned from that role in 2017 after it emerged she had conducted unauthorised meetings with Israeli officials
- Tough stance on immigration has made her a popular figure with grassroots Conservatives
- Voted against gay marriage and has advocated bringing back the death penalty in the past but does not support it now
The report, carried out by the government's independent adviser on standards, Sir Alex Allan, has not been published.
But one source said it had concluded that the "home secretary had not met the requirements of the ministerial code to treat civil servants with consideration and respect".
They added that the investigation had found evidence of bullying, even if it had not been intentional.
Another source who saw the report called it "unambiguous in stating that Priti Patel broke the ministerial code and that the prime minister buried it".
A spokesman for the home secretary said she had always denied the allegations and that there had never been any formal complaints made against her.
A different government source has suggested that the report also paints an unflattering picture of how Ms Patel was sometimes treated.
What is the ministerial code?
- Government document setting out "expected standards" of behaviour in office, which include "consideration and respect" for civil servants and other colleagues
- In the foreword, Boris Johnson says: "There must be no bullying and no harassment."
- Ministers are normally expected to resign if they are found to have broken the code
- There are no known cases of a minister staying in post following a breach
- Ministers who have stepped down include Liam Fox, over taking a friend and lobbyist on official trips, and Mark Field, who grabbed a climate protester
- The code has existed since the Second World War but was not made public until 1992
The report is understood to have looked at Ms Patel's behaviour at three different government departments - the Home Office, Work and Pensions and International Development.
The evidence gathering was completed several months ago, but Downing Street has delayed giving a decision on the findings.
The prime minister is the ultimate arbiter of the ministerial code, and there is no requirement on the government to publish Sir Alex's report.
The BBC understands there have been conversations in government this week about how to manage the situation, with suggestions that Ms Patel may be given a reprimand, or be asked to apologise, but keep her job.
'Strong and decisive'
Earlier this week former Cabinet Secretary Sir Mark Sedwill suggested there could be a "wider range of sanctions", telling MPs: "I don't think it should be binary between let off or sacked."
Dave Penman, general secretary of the FDA senior civil servants' union, said "thousands" of civil servants would be asking what "message" it would send if the government suggested Ms Patel did not have to resign over a "little bit of bullying".
He described the system as not "fit for purpose", adding: "We need an independent process that's not relying upon a prime minister making a political judgement rather than judging based on the evidence."
But several Conservative MPs have offered Ms Patel their support.
Tom Tugendhat tweeted that she was popular "across" the party because she was "hardworking, determined and has been very kind to many".
Another Tory MP, Julie Marson, said the home secretary was doing a "huge job", adding: "Like many women operating in a man's world, you have to be strong and decisive."
Former Conservative Party leader Sir Iain Duncan Smith said it was "really important" that the report is "properly published".
He added that there may be a balance in the report "between poor behaviour of the civil servants at that stage in charge and also issues or questions over the behaviour of the minister".
Labour called on the Committee on Standards in Public Life to investigate Ms Patel, but the committee chair Lord Evans of Weardale said his body could not look into individual alleged breaches of the rules.
He added there were "weaknesses" in the current standards structures and that his committee was conducting a review into the system.