Lithuania was moved into the grey area after failing to provide data, according to the ECDC.
Those arriving from grey area countries within the EU might be subject to stricter requirements.
Justina Petraviciene, spokeswoman for Lithuania's National Public Health Center, told BNS the center is now looking into why Lithuania was deemed as having failed to provide data.
"The experts said they had provided data as usual. My colleagues are now in contact with the ECDC to find out the reason why the data is not seen," Petraviciene said.
Meanwhile, Lithuania is around the middle in the ECDC's statistics table where July 5-18 epidemiological data from 29 European countries are compared. The country's 14-day rate stood at 71 per 100,000 at the time.
This rate now stands at 91.4, according to the latest figures from Lithuania's statistics service, Statistics Lithuania.