Many nations fear the spreading conflict in Ethiopia - Africa's second-most-populous nation and a regional diplomatic heavyweight - might further destabilise an already fragile region.
The seven people being expelled include the country heads of the United Nations Children's Fund (UNICEF) and the head of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA). The seven have 72 hours to leave, the ministry said in a statement, accusing them of "meddling" in internal affairs.
A statement from UN Secretary General Antonio Guterres said he was "shocked" by the expulsions and added: "We are now engaging with the Government of Ethiopia in the expectation that the concerned UN staff will be allowed to continue their important work."
The Ministry of Foreign Affairs did not immediately respond to requests for comment.
Conflict erupted between federal forces and those aligned with the Tigray People's Liberation Front (TPLF), the political party that controls the region, in November.
Tigrayan forces retook most of the region at the end of June, and then pushed into the neighbouring regions of Afar and Amhara, forcing hundreds of thousands of people there to flee their homes.
On Tuesday, UN aid chief Martin Griffiths, the head of OCHA, said a nearly three-month-long "de-facto blockade" of Tigray's borders has restricted aid deliveries to 10 per cent of what is required.
"This is man-made, this can be remedied by the act of government," Mr Griffiths said, noting nearly a quarter of the children in Tigray are malnourished.
Five of the seven people being expelled work for OCHA, while a sixth works for UNICEF and the seventh works for the Office of the High Commissioner for Human Rights, which is conducting a joint investigation with Ethiopia's state-appointed human rights commission into reports of mass killings of civilians, gang rapes and other abuses in Tigray.
Ethiopian authorities previously accused aid workers of favouring and even arming Tigrayan forces, although they have provided no evidence to support their accusations.
In August, Ethiopia suspended the operations of the Dutch branch of medical charity Medecins Sans Frontieres (MSF) and the Norwegian Refugee Council, accusing them of arming "rebel groups".
So far, 23 aid workers have been killed in Tigray.