https://www.united.com/ual/en/us/fly...b-and-lounges/
Admittance
A valid United Club membership card or one-time pass, a same-day boarding pass and a government-issued photo ID (such as a driver's license, passport or military ID), or other credentials are required for admittance to United Club locations.
Effective November 1, 2019, United Club customers, including members and their guests, and one-time pass holders will need to provide a same-day boarding pass for travel on United, Star AllianceTM or a contracted partner operated flight for entry into all United Club locations. Admittance to United Club locations is permitted only at the departure and arrival airports for United, Star Alliance or a contracted partner operated flights.
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Seemed pretty clear