Military charity Help for Heroes says 142 staff roles are at risk, as its income has dropped by nearly a third during the pandemic.
The charity, which supports wounded veterans and their families, says there are likely to be about 80 redundancies.
It relies on donations for 97% of its funding, but its fundraisers have been cancelled or postponed since March.
Charity chief Melanie Waters said: "These tough decisions have been made to protect the future of the charity."
Three Help for Heroes recovery centres - in Yorkshire, Devon and Essex - will remain closed indefinitely as Help for Heroes focuses on face-to-face community and online-based support.
The charity said demand for its services rose by 33% during May and June - compared to the same period last year - as the consequences of the national lockdown impacted on veterans' mental health.
Requests for help with physical conditions also increased by nearly a third over the same period.
Meanwhile, the charity - which furloughed 130 staff at the start of the pandemic - said it anticipates funding will remain down by around a third for the foreseeable future, as the economy struggles to recover.
Ms Waters said a major restructure was the only way the charity could continue with its work.
"In 2007, we made a promise on behalf of the nation to provide lifetime support to wounded veterans, and their families, and we are striving to keep that promise," she said in a statement on their website.
"The crisis has had a devastating impact on the whole UK charity sector, with lasting consequences, and it has hit us hard."
The charity said it was working closely with the Ministry of Defence "to provide core recovery activities for wounded, injured or sick service personnel" and hoped to reopen its Tedworth House recovery centre in Wiltshire, with social distancing measures in place - as well as their community office in Wales.
Last year, the charity - which was set up in 2007 by former Army Captain Bryn Parry and wife Emma - raised around £27m.
"We remain absolutely committed to our wounded and their families and will continue fighting for, and changing the lives of, those we support for as long as they need it," said Ms Waters.