Millions of commuters were forced to find alternate means of transportation on Monday morning as London's subway network came to a screeching halt.

Union workers for the city's rail system, known as the "Tube," kicked off a week of travel strikes that could spread across the country, affecting both train and air passengers. The London Underground strike by staff in the National Union of Rail, Maritime and Transport Workers unionand the Transport Salaried Staffs' Association is the latest move in a dispute over staffing levels and the recent closure of ticket offices.

John Leach, RMT London regional organizer, told the BBC Radio 4's Today program that the cause of the 24-hour strike was Transport for London (TfL) closing a number of station control rooms and laying off 834 workers, changes that had led to safety concerns about overcrowding at Tube stations.

"This action has been forced on us by savage cuts to jobs that have reduced London Underground to an under-staffed death trap at a time of heightened security and safety alert," said RMT General Secretary Mick Cash in a statement. "RMT members will not stand idly by while they see day in and day out the safety regime on the tube being slashed to ribbons."

TfL said it agreed that more staff were needed in stations, and it had already started recruiting 200 extra workers. But representatives for the unions argued that 200 was not enough.

As subway cars stood at a standstill on Monday morning, millions of displaced Londoners took to the street to walk, drive, bicycle, Uber, and wait in line for overcrowded buses. During rush hour, many major roads in the city were gridlocked, according to reports.

"I'm giving up on even trying," said software developer Rajiv Perseedoss, whose commute was disrupted by the strike, to Reuters. "I'm not a Tube worker, I don't know about their conditions, but whatever it is, they can't take it out on everybody."

The action was criticized by London Mayor Sadiq Khan, who described the strike as "totally unnecessary."

Ending the strike, Mr. Cash of RMT said, is the responsibility of Mr. Khan and other government officials.

"The solution is in the hands of the Mayor and ‎his officials," Cash said, noting that the union was available for further talks. "They need to come up with serious and urgent plans designed to address the core issues at the heart of this dispute and a schedule for staffing back up on the stations to a level our reps believe is safe and sustainable."

Some Conservative lawmakers have called for the government to implement new laws to curb strikes. Such demonstrations, they say, cost millions of pounds and hurt the city's reputation as a major economic and financial powerhouse.

Get the Monitor Stories you care about delivered to your inbox. By signing up, you agree to our Privacy Policy

"At a time when the government is doing everything it can to show Britain is open for business post Brexit, a resurgence in union activity doesn't help that message," lawmaker Tim Loughton told the Telegraph.

This report includes material from the Associated Press and Reuters.