Currently, wearing facemasks is recommended but not mandatory for those who have the COVID-19 immunity certificate.
As of October 1, everyone will be required to have a face covering on in closed public settings, such as in shops or during events, even if they are only open to those with the certificate.
The requirement will not apply to people who cannot wear a mask for medical reasons, where a service cannot be provided to a customer wearing a mask, and while eating and drinking in bars, cafes or restaurants.
Prime Minister Ingrida Simonyte confirmed later that face coverings will also be compulsory at work "when people work in close contact in closed spaces".
She added that the government "strongly" recommends that people work remotely where possible.
At schools, facemasks remain mandatory for all students except primary classes, according to the prime minister.
The tightening of the requirements comes amid a rapid spread of the Delta variant and the worsening epidemiological situation in Lithuania.
Currently, 67.7 percent of the Lithuanian population is immune to COVID-19, either through vaccination or infection, but the number is still insufficient to control the spread of the virus, according to the government.
Last week, Lithuania moved into the worst "black" zone under the color-based pandemic classification system.
The latest official statistics showed on Wednesday morning that Lithuania's daily infection count had hit 1,847 cases and 14 people had died in the past 24 hours,
Lithuania’s 14-day coronavirus infection rate has risen to 656.3 cases per 100,000 people, and the share of positive tests for the past 7 days has gone up to 7.2 percent.