Some 600 staff are affected
Cancer Research UK is considering closing 200 of its high-street stores.
It comes as part of a major restructure which is looking to close 90 of its 519 high street stores by May, and 100 more by April 2027.
The move will affect 600 members of staff and 3,000 volunteers.
The charity said it will support employees and offer redeployment opportunities where possible.
The charity said that in common with many high-street retailers, it was facing rising costs, inflationary pressures and shifting consumer habits, including higher National Insurance contributions, reduced footfall on the high street and increased competition from online resale platforms.
However it is still planning to open an additional 12 out-of-town superstores over the next two years to add to the 46 it already operates.
The charity hopes the move will result in an increased financial contribution from its retail operation of about £12.4m over the next five years.
Michelle Mitchell, chief executive of CRUK, said: “A smaller, high-performing retail operation will mean we will fund more life-saving cancer research and better serve our customers, staff and volunteers,” she said.
“This news will be difficult. Our decisions have been taken after serious consideration. We’re committed to supporting everyone affected by these changes, and will provide clear information and support throughout the process.”