The London Underground shuddered largely to a halt on Monday, as one of the world’s biggest public transit systems was hit by a labor strike that is scheduled to continue until Friday morning, affecting millions of travelers. Stations on the underground network, known as the Tube, were shuttered, and buses and trains running above ground were more crowded than usual, while many commuters walked or cycled into the city. Trams and the Elizabeth line, a relatively new route running from the east to the west of London, were operating on Monday. Still, with more than four million Tube journeys made every weekday, stores, bars, restaurants and other businesses were braced for financial losses if, as expected, more people work remotely and avoid central London. Against a backdrop of rising food and energy costs, labor unrest has afflicted several parts of Britain in recent years, including a long-running dispute by garbage collectors in Birmingham, the country’s second most populous city.