By Dave Sebastian

Booking Holdings Inc. said it plans to cut up to a quarter of Booking.com's global workforce, or roughly more than 4,000 people, and restructure the company as the Covid-19 pandemic continues to batter travel demand.

The online travel agency, which also operates Kayak, OpenTable, Priceline and Agoda, said it is in talks with works councils, employee representatives and relevant organizations as it decides on the timing, number of affected employees and other parts of the cost-reduction measures. The Booking.com unit employs more than 17,000 people, a company spokeswoman said.

The Norwalk, Conn.-based company said it expects to finalize the plans on a country-by-country basis starting in September and send all layoff notices by the end of the year. Booking Holdings operates in more than 65 countries and employed more than 26,000 across its brands as of the end of last year.

"The travel industry remains under significant pressure," Glenn Fogel, president and chief executive, told employees in a video Tuesday. "At Booking.com this has hit, and will continue to hit, our business hard."

Booking Holdings has also cut jobs at its other brands, including 1,500 in Asia at Agoda in May, the spokeswoman said.

Booking Holdings derives most of its revenue from travel-reservation commissions. In March, when lockdown measures escalated in the U.S., the company received more cancellations than new bookings. It is set to report second-quarter results on Thursday, detailing the full extent of the effects of the pandemic.

Booking's layoffs come as other travel-related sites are also moving to cut costs to stay afloat. Tripadvisor Inc. has moved to eliminate 900 jobs, or about a quarter of its workforce, as it shrinks its operations.

Expedia Group Inc. last week reported a second-quarter loss as gross bookings fell 90%, though it noted that cancellations moderated in May and June from the troughs of April. But with some U.S. states seeing a resurgence in Covid-19 cases, the path to travel recovery remains uncertain.

"We will have a bouncy recovery -- there's no question," Peter Kern, Expedia's vice chairman and chief executive, said on a conference call last week. "We expect this not to be a linear recovery, obviously, and we expect some bumps in the road."

Write to Dave Sebastian at dave.sebastian@wsj.com