Travelers from Britain, Canada, Australia, and New Zealand can now enroll in Clear Secure, the American tech firm that allows people to pay for expedited clearance at U.S. airports, the company confirmed Friday.

Summer travelers are facing uncertainty as the clock winds down on a possible strike by Air Canada flight attendants, which the airline said would force it to cancel almost all of its scheduled flights as soon as Saturday.

Flight attendants are demanding better wages and compensation for unpaid work. Currently, Air Canada only compensates flight attendants for the time they are in the air, but its attendants are seeking pay for the work they do before take-off and after landing, too.