The Portuguese government's efforts to reorganize the debt-heavy public transport sector continue to meet resistance, with Lisbon subway workers walking off the job for the fourth time this year.

The Metropolitano de Lisboa shut down for 24 hours Tuesday as staff kept up their fight to stop the government granting private companies concessions to operate services. The concessions are expected to be announced within weeks.

Subway staff have on average staged a strike once a month since 2012, when the plan was announced.

Workers with the Lisbon bus company Carris and national rail company Comboios de Portugal, both of which are also deep in debt, have also held regular strikes.

Portugal's high public debt forced it to request a 78 billion euros ($87 billion) bailout in 2011.