The Olympics fiasco could hurt G4S' role in the public sector in the UK, making them a less tempting choice for government or councils.
Security company G4S has admitted the failure to fulfil its Olympics contract cost it in the region of £50 million.
G4S is to donate £2.5 million to the Armed Forces after 18,200 military personnel were drafted in for London 2012.
Nick Hardwick, the Chief Inspector of Prisons, said it was "simply not acceptable to initiate force for such purposes".
We were very concerned to find that force had been used to effect the removal of a pregnant woman, using non-approved techniques.
There is no safe way to do this while protecting the unborn child and it is simply not acceptable to initiate force for such purposes.
The pregnant woman's husband had been disruptive the night before his family's planned removal from the Cedars centre in Pease Pottage, West Sussex "shouting and kicking doors, causing some damage", the report found.
At one point it was judged that he had been trying to separate healthcare staff offering to examine his wife to take them hostage.
Staff were sufficiently concerned by his behaviour to take him to the 'cool down' separation room in full personal protection equipment before his removal.
Judith Dennis, of the Refugee Council, said the case was "shocking" and called for the UK Border Agency (UKBA) to heed the report's recommendations, which include that force should only ever be used against pregnant women and children "in order to prevent harm".
The pregnant woman facing removal from the UK was given a wheelchair to assist her in the departures area of the Cedars centre in Pease Pottage, West Sussex, inspectors said.
But when she resisted "substantial force" was used by G4S staff and the wheelchair "was tipped up with staff holding her feet".
"At one point she slipped down from the chair and the risk of injury to the unborn child was significant," the report said.
"There is no safe way to use force against a pregnant woman, and to initiate it for the purpose of removal is to take an unacceptable risk."
A pregnant woman in a wheelchair was tipped up and had her feet held by staff from the firm behind the Olympics security shambles as she was forcibly removed from the country, inspectors have said.
G4S staff used substantial force and unofficial techniques and the "risk of injury to the unborn child was significant", the first report on a new pre-departure centre used to remove families from the UK found.
A G4S spokesman confirmed its staff were involved in incident.
David Taylor-Smith and Ian Horseman Sewell, who quit their roles at G4S on Friday, are not expected to receive any pay-offs outside of notice entitlements within their contracts.
G4S chief executive Nick Buckles kept his job on Friday despite the resignation of two other key company directors in the wake of a botched Olympics contract.
Did you know that his salary is close to £1 million, his business hero is Margaret Thatcher and he used to be a postman?
G4S bosses were right to quit over the Olympics fiasco, London Mayor Boris Johnson told LBC radio on Friday.
– BORIS JOHNSON
The rank and file, the troops on the ground, did a wonderful job, but when you look at what happened in the management of those hordes of G4S employees who did a great job, I'm not going to try and persuade them to stay this morning."
The right decision bearing in mind the G4S fiasco . Its not closure. They must waive their fee and pay compensation # g4sFrom @Keith_VazMP on Twitter:
Labour MP Keith Vaz said the resignation of two G4S directors on Friday was "the right decision".
G4S says it will appoint a chief operating officer to work closely with chief executive Nick Buckles on customer service and project delivery.
It has also promised to carry out more rigorous risk assessments of new contracts and will demand board-level oversight on contracts where annual revenues exceed £50 million.
G4S said its board had decided that it was in the best interests of the company and its shareholders that Buckles remains as chief executive.
Buckles, who admitted to MPs that the Games staffing episode had been a "humiliating shambles", was not guilty of any significant shortcomings in his performance, the company said.
G4S have explained why chief executive Nick Buckles remains in is post despite the company's Olympics failure in a statement.
– G4S statement
"Whilst the CEO has ultimate responsibility for the Company's performance, the Review did not identify significant shortcomings in his performance or serious failings attributable to him in connection with the Olympic contract."
Two G4S directors have resigned in the wake of an independent review into the company's botched Olympic Games contract.
Chief operating officer David Taylor-Smith and Ian Horseman Sewell, who is head of global events, are to carry the can for the fiasco but chief executive Nick Buckles will remain in his post.
The report by PwC found that monitoring and tracking of the security workforce was inadequate and that management failed to appreciate the scale and exact nature of the project.
G4S fulfilled 83% of contracted shifts at the Games, failing to provide all of the 10,400 contracted guards and forcing the Government to step in with military personnel.