"The university is requesting the union surrender occupancy of the Composite Building within seven days," said Steve Lo Chit-ki, chairman of the HKU accommodation committee, in a letter to the university's student societies and associations.
Members of the union will have to submit an application to the estate office if they want to enter the building to clear out union or personal belongings in the coming two months.
Student societies and associations under the union can still use offices in the Composite Building after registering with the committee before Wednesday and making a "mutual agreement on terms and conditions with the university."
Former chief executive Leung Chun-ying said yesterday that there were comments that the students' union system should not be blamed because of the mistakes of its current cabinet.
But Leung cited editions of the student newspaper Undergrad in 2013 and 2014, which included articles on Hong Kong nationalism and statements that the Hong Kong nation decides its own fate.
"HKUSU Council's decisions and statements last week were not a one-time incident, and it was certainly not a coincidence," Leung wrote on his Facebook.
On Wednesday, Secretary for Security Chris Tang Ping-keung said law enforcement authorities may look into the case under the Societies Ordinance.
A legal expert said the union may be eradicated if police decide to get rid of its society registration, as the societies officer can cancel the registration of any organization after consulting the secretary for security.
HKU scrapped recognition of the union on Tuesday for passing a motion appreciating the "sacrifice" of Leung Kin-fai, 50, who allegedly stabbed an officer in Causeway Bay on July 1 before killing himself.
The union's council retracted the motion a day later, publicly apologized and resigned en masse.
Separately, Lingnan University became the fifth university to distance itself from its student unions by refusing to help them collect fees, after City University, Chinese University, HKU and Polytechnic University. In an internal e-mail, it said some students, parents and the public said it was "misleading and inappropriate" to collect student union membership fees alongside tuition fees.
The NHS said the devices used to monitor blood-oxygen levels at home may give inaccurate readings for people with darker skin.