People arriving in Finland from coronavirus "risk countries" have to self-isolate for 14 days or risk a fine or up to three months' imprisonment, ministers announced on Monday.
Until now the Nordic country has relied on arrivals voluntarily quarantining themselves, with no sanctions in place for those who do not follow the recommendation.
Announcing that the new rules will be implemented "as soon as possible", health minister Krista Kiuru also said arrivals may face compulsory coronavirus testing.
The decision follows a number of reports in recent days of planes arriving from Eastern European and Balkan countries carrying passengers who were either found to be infected or who refused to be tested on arrival.
After a number of weeks early in the summer with only a trickle of cases, 135 new infections have been recorded in the past seven days.
"The number of infections has surprised us all," Kiuru told a press conference on Monday, while health officials blamed arrivals from overseas for some of the increase in cases.
"We have had discussions as to whether we can stop flights from risk countries. We are looking into it," Kiuru said.
The measures will apply to arrivals to all countries except those on Finland's green list, which are those with fewer than eight new cases per 100,000 population in the last two weeks.
Currently 25 countries are deemed safe, including Ireland, Japan, Greece, Cyprus and Uruguay.
According to the World Health Organization, Finland has one of the lowest virus incidence rates in Europe, with just three new cases per 100,000 population.