She played an instrumental role in the labour strike in February 2020 to demand full border closure in response to the COVID-19 outbreak in Hong Kong.

[2] The Hospital Authority Employees Alliance (HAEA) was founded in the call for forming labour unions to launch a city-wide strike to pressure the government,[3] in which Yu became the chairwoman.

[4] Following Chief Executive Carrie Lam's announcement to close four borders to the mainland, rather than a full closure demanded by the HAEA, the union launched a labour strike for five days between 3 and 7 February 2020.

[1] as well as On 7 February, the HAEA fell 2,000 votes short of the target it set to extend industrial action into middle of next week.

[8] Yu participated in the 2020 Hong Kong pro-democracy primaries and received 2,493 votes, winning against incumbent lawmaker Joseph Lee in the Health Services functional constituency.

[9] On 6 January 2021, Yu was among 53 members of the pro-democratic camp who were arrested under the national security law, specifically its provision regarding alleged subversion.