London's tube strike has been denounced as "economic vandalism" by a newly knighted senior Conservative MP.
Sir Richard Ottaway, the MP for Croydon South, slammed the joint industrial action between the Rail, Maritime and Transport Workers Union (RMT) and the Transport Salaried Staffs' Association during Prime Minister's Questions in the House of Commons.
The strikes, which are over job losses, have meant that thousands of commuters in the capital have been delayed from getting to work.
"London is a 24/7 global city and the commercial centre of the Western World," said Ottaway.
He added: "With the economy growing and unemployment falling, would [the Prime Minister] agree that the efforts of the RMT union to bring London to a halt through the tube strikes is nothing short of economic vandalism."
David Cameron claimed there was "absolutely no justification" for a strike and stressed that the capital "needs a modernised tube line working for the millions of Londoners who use it every day".
He added: "I unreservedly condemn this strike. I hope the Leader of the Opposition [Labour's Ed Miliband] will [also] unreservedly condemn this strike."
But Miliband decided to immediately challenge the Prime Minister about the UK's recent floods and storms, claiming that many of those affected "feel the government's response has been slow".
The comments come after Bob Crow, the general secretary of the RMT, justified the industrial action.
"More and more people want to use the underground and you're going to take around 800 jobs away to deal with those people," said Crow.
He added: "[The ticket office supervisors] play a crucial role. They are visual, they've got experience, and when the [7/7] bombings took place by the vicious terrorists in London, these are the people who came from behind the back of the booking offices to support those group of passengers who were travelling around London to get them to a safe place."
London Underground has said it will enlist volunteers to help run the tube network throughout the industrial action.
"Our customers and staff are at the very centre of our plans for London Underground," said Mike Brown, London Underground managing director.
"All Tube stations will remain staffed and controlled at all times when services are operating, and we'll be introducing a 24-hour service at weekends during 2015.
"In future, there will be more staff in ticket halls and on platforms to help customers buy the right ticket, plan their journeys and to keep them safe and secure.
"We're committed to implement these changes without compulsory redundancies and there'll be a job for everyone at LU who wants to work for us and be flexible."