David Evans, general secretary, of the 27,000 strong Prison Officers' Association, has written to Richard Tilt, director-general of the Prison Service, to express his concern about the security and safety of jails in England and Wales. He says the crisis has been heightened by a dramatic increase in the jail population to a record 60,000.
Mr Tilt has agreed to discuss the issue next week and has set up a special meeting next month to examine the problems caused by over-crowding.
Mr Evans wrote to Mr Tilt last week on behalf of the POA's National Executive Committee to express "their anxiety and concerns over the increasing prisoner population.
"We are seeking an urgent meeting with you to discuss this issue as it impacts greatly not only on the penal estate but on the safety and security of everyone working within penal institutions and indeed, the general public."
The committee's warning follows the publication of a POA report earlier this week which claimed security at Broadmoor special hospital is at "breaking point". The report was sent to Stephen Dorrell, the Secretary of State for Health.
The Prison Service is trying to gain permission to moor a floating jail off Portland, Dorset, and convert a former Pontin's holiday camp, near Morecambe Bay, Lancashire, into a make-shift prison, to ease the crisis. Mr Evans added the Prison Service had shed 900 staff last year: "Now they are having to launch a massive recruitment programme. That's a crazy kind of management."
He warned there was a growing sense of unease in many prisons. "It has become a powder keg that could blow at any time and place".
A Prison Service spokeswoman, said: "The director- general has taken the letter seriously and has agreed to meet and discuss the issue."