LloydsPharmacy will close 190 stores across England due to changes in Government policy, with its parent company blaming funding cuts and business rates for the move.
Cormac Tobin, managing director at LloydsPharmacy owner Celesio UK, said the closures were in response to "the dramatic funding and reimbursement cuts over the past 24 months".
"Community pharmacy needs to adapt to the changing requirements of patients and the NHS, indeed it should be part of the solution to an overstretched health service," Mr Tobin said.
"To achieve this, we need a new operational framework that creates a thriving pharmacy network that continues to offer essential integrated healthcare and is rooted in local communities."
A leaked internal memo to staff - which was verified by a spokesman for Celesio UK - said the business has been hit by pharmacy funding cuts, as well as business rates and the apprenticeship levy, which had made "market conditions challenging".
A spokeswoman for LloydsPharmacy owner Celesio UK did not confirm the number of staff that could be affected, saying some may be deployed to other locations.
Mr Cormac said the company would be taking steps to support staff and minimise disruption for patients.
Julie Cooper, Labour's shadow minister for community care, said: "This is a devastating blow for Lloyds Pharmacy staff and their patients right across the country.
"The Government is taking hundreds of millions pounds of support away from pharmacies, and now we see that it is patients who will pay the price."
Ms Cooper has urged ministers to outline plans to support "the hundreds of Lloyds pharmacy jobs that are now at risk" and explain what support will be put in place for patients reliant on their service.
"The Tories are prioritising saving money over care. They cannot just expect elderly patients to get their prescriptions via an online service, without any support with their medication," Ms Cooper added.
A Number 10 spokeswoman said there were measures in place to ensure people could access a pharmacy.
The spokeswoman said: "There are almost 12,000 private pharmacies in England and these closures today make up just 1.6% of the number.
"We don't have full information on the announcement as yet, but we do make sure that patients can access pharmacists where they need to."