Unite the Union says it is due to meet the DoI today but that no new offer has been put on the table.
Bus drivers began their strike on Saturday and are due to be out for the rest of the week.
In a statement, Unite said: “Let me be absolutely clear before the narrative starts — there is no new offer on the table.
“Nothing has been revised. Nothing has been improved. Nothing formal has been put to us.
“So today is an opportunity for the department to decide whether it genuinely wants to resolve this dispute or simply continue managing headlines.
“Our drivers have been consistent from day one. Fair consolidated pay. Recognition of all hours worked. Parity and respect.
“We will attend in good faith, as we always do. But progress requires movement.”