There are 116 Blacks stores and 256 Millets branches in the UK
Blacks Leisure has announced plans to close 89 stores across the group that have not "traded profitably for years".
The firm, which operates Millets, Blacks and O'Neill shops, also said it plans to lay off 50 staff at its Northampton head office.
Last week, it called in administrators to its 11 O'Neill boardwear stores - threatening 90 jobs.
It also said a drop in sales during the downturn meant it would breach the terms of its bank loans.
The company did not give an indication of how many jobs would be lost by the store closures.
It described the closures and job losses at the head office as "highly regrettable", but added that "both actions will ultimately strengthen the business and help ensure that a successful and profitable outdoor retailer emerges from the current restructuring process".
The group made a loss of £6.8m in the year to 28 February.
It operates 256 Millets shops, 116 Blacks Outdoor outlets and 32 Freespirit stores.