Holiday firm Thomas Cook says it is planning to axe 2,500 UK jobs to "secure" its future.
It plans to consult on proposals to close 195 of its 1,069 high street travel agencies, with the full details being announced at a later date, though a union representing staff has already spoken of its fury at the scale of the cuts.
It is understood that many of the stores to close operate under the Co-Operative brand.
Thomas Cook is also planning to shut its Accrington office in the North West in a move impacting around 100 roles while administrative and managerial jobs are at risk across its head office in Peterborough and its Preston site.
The job losses amount to 16% of its 15,500 workforce in the UK and Ireland.
In a statement, the company said: "As Thomas Cook UK & Ireland continues to focus on the turnaround of the business it has today entered a 90 day consultation process with a number of its UK employees on the next phase of the three-year programme to transform its operations.
"The need to evolve the UK business has been a clearly stated goal, accelerated by the appointment of Peter Fankhauser, an experienced Thomas Cook leader as UK CEO.
"The UK business needs to reduce cost to ensure back-office costs are not passed on to customers and that the necessary operational changes are made to reflect evolving customer needs and purchasing requirements."
It continued: "The company has 1,069 stores in the UK, making it the largest high street travel retailer. A number of these stores do not meet the performance targets of the business and are in communities where Thomas Cook has more than one retail outlet."
Mr Fankhauser added: "Thomas Cook is a much loved brand that needs to make the proposed changes to secure our future and provide continued employment for many thousands across the UK and better meet the needs of our customers going forward.
"We firmly believe these proposals will mean a better - more profitable - Thomas Cook that continues to be a major employer in the UK and offer the widest range of holidays for travellers and voyagers in the future.
"We are already consulting with our Unions and employee representative bodies to minimise the impact of these changes and I am speaking personally to all employees today to provide information and support through this period of consultation."
Thomas Cook's transformation plan, under which it had already cut 168 stores and 1,100 jobs, was blamed for deeper losses in its last financial year.
The 171-year-old company reported a statutory loss of £590m for the 12 months to the end of September - worse than the £518m loss recorded the previous year.
Thomas Cook was under pressure to tighten its purse strings at a time of a slowdown in consumer spending and changing holiday habits.
The Transport Salaried Staffs Association (TSSA), which represents employees, said it was "shocked and angry" at the scale of the job losses.
General secretary Manuel Cortes said: "This constant policy of slash and burn, with the axing of one in four stores and the loss of jobs, is simply self-defeating.
"The company needs new products if it to come to come to terms with the age of the internet and prosper in the 21st century."
Thomas Cook also confirmed it planned to change staff terms and conditions for remaining workers.
Sharon Ainsworth, national officer of Usdaw, said: "Even those who are not at risk of redundancy are facing the prospect of cuts to their benefits packages, following a number of cost-cutting proposals which the business has put forward.
"We will be examining these proposals closely and will defend our members' interests throughout this uncertain time."