A strike has shut the Lisbon subway for the second time in a month and the 11th time in a year as militant trade unions continue to fight the government's public transport policy.

The Federation of Transport and Communications Unions called the 24-hour walkout Thursday. It accuses the center-right government of reducing staff levels and infrastructure investment ahead of privatizing public transport companies.

The government says it has to cut expenditure at the companies, which are close to 16 billion euros ($20 billion) in debt after decades of taxpayer subsidies.

The Metropolitano de Lisboa carries on average around 370,000 passengers a day. The strike by most of its 1,450 employees shut down services, leaving many commuters in long queues for buses.