TUNIS (Reuters) - Tunisia’s powerful UGTT union called on Saturday for another national strike for two days next month to press its demand for higher wages for 670,000 public servants, the UGTT chief said.

Rail, bus and air traffic and all services stopped in Tunisia and street protests drew thousands on Thursday in a one-day nationwide strike to challenge the government’s refusal to raise salaries.

“As negotiations with the government failed and the purchasing power has deteriorated significantly, UGTT decided to approve a nationwide strike on Feb. 20 and 21,” UGTT chief Nourredine Taboubi told reporters.

The decision will raise the pressure on the government which is struggling to revive the faltering economy.

The government is also under pressure from the International Monetary Fund to freeze public sector wages, the bill for which doubled to about 16 billion dinars ($5.5 billion) in 2018 from 7.6 billion in 2010, as part of measures to reduce its budget deficit.

But the UGTT says the monthly average wage of about $250 is one of the lowest in the world, while the state Institute of Strategic Studies says real purchasing power has fallen by 40 percent since 2014.

The government had said it does not have the money to pay for the increases strikers want, worth about $850 million in total.

Government spokesman Iyad Dahmani said that increase would lift annual inflation to 10 percent from 7.4 percent.

An economic crisis has eroded living standards for Tunisians and unemployment is high as political turmoil and lack of reforms have deterred investment needed to create jobs. That has forced the government to launch austerity measures to please donors and lenders including the IMF.