The Restaurant Group (TRG) will not reopen 100-120 sites following lockdown, with job losses of 2,000-3,000 expected.
The majority of sites affected are understood to be operating under the group's Frankie & Benny's brand, as well as Garfunkel's.
In an email to staff seen by the BBC , TRG said many sites are "no longer viable to trade and will remain closed permanently".
TRG filed notice to put Chiquito into administration in March, a move that will permanently close the majority of the 81 Tex-Mex brand's sites.
The Restaurant Group had already announced last year that it would close more than 150 outlets, including Chiquito and Frankie & Benny's sites, as part of a restructure over the next six years, following its acquisition of Wagamama for £559m.
The group raised £57m through a share placing in April aimed to provide the company with "sufficient" liquidity to continue to operate through the coronavirus crisis. However, it issued a "pessimistic scenario for the current financial year" at the time, with the possibility that only 400 of its 600 sites will reopen.