"The [UGTT] union is protesting against the delay in the payment of wages and bonuses," said Hayat Chamtouri, a spokesperson for the company said.
"The financial situation in the company is really difficult," she added.
The transport strike is a show of strength for the powerful UGTT union, which has pledged to hold a series of protests.
The strike sparked anger among thousands of people struggling to find transport in the capital.
"Today, we do not find milk, oil, sugar, or coffee. Also now we do not find buses that take us to work. Tunisia has become an unbearable hell," said Nejia, a woman waiting at a bus station.
In the poor Intilaka neighborhood, people blocked roads to protest against the strike.
The strike will increase pressure on the government of President Saied, who is facing growing opposition 17 months after seizing executive powers in a move his opponents described as a coup.
The union, with 1 million members, has approved a two-day strike by air, land and sea transport workers on Jan. 25 and 26, to protest against what it called "the government's marginalization of public companies."
Tunisia, is financially struggling, seeking a $1.9 billion loan from the International Monetary Fund in exchange for unpopular reforms including spending cuts, the restructuring of public companies and reductions in energy and food subsidies.
The economy minister Samir Saeed said last month that Tunisia will face a difficult year with an inflation rate that will exceed 10 percent.