Workers have been told by managers to either stay and work or lose their jobs, civil society organisations said last month, citing miners and union representatives and demanding an end to the approach.
"All mining companies that have confined workers to the operating site are granted a one-month moratorium to return to normal operation," Labour Minister Nene Ilunga Nkula said in the letter, dated July 13, which she shared on Twitter on Tuesday.
Mining companies must provide healthcare for workers and their families, as well as decent housing and a healthy diet for confined workers, Nkula said.
Congo is Africa's top copper producer and the world's main source of cobalt, accounting for two-thirds of global supplies of the metal used in smartphones and electric car batteries.
Mines minister Willy Kitobo Samsoni has said full mine shutdowns would trigger a catastrophic economic and social crisis in the country, with the industry contributing 32% of its GDP and 95% of export revenue in 2018.
Companies mining in Congo's southern copper belt include Glencore subsidiary Katanga Mining, China Molybdenum's Tenke Fungurume, MMG, and Chemaf, while Ivanhoe Mines is developing two copper mines there.
Six workers at Glencore's Kamoto Copper Company (KCC) mine in Lualaba province have tested positive for the novel coronavirus, KCC said a week ago.
Glencore said KCC does not confine workers on site.
Ivanhoe locked down its Kamoa-Kakula project, moving workers into mine-site accommodation, on April 3. On June 1, the company allowed the project's Congolese employees to resume commuting to site from neighbouring communities.
Companies in Lualaba have a month from July 2 to prepare sanitation measures and release all workers confined for more than a month. In Haut-Katanga the period runs from July 6, the letter said.
(Reporting by Hereward Holland; Editing by Helen Reid, Alison Williams and Barbara Lewis)