The National Transport Authority has confirmed that it has deducted €423,000 from Dublin Bus's public subvention because of the three-day strike in August.
A spokesperson for the NTA confirmed that Dublin Bus would only receive subvention for services that were actually provided.
Last week, bus drivers belonging to SIPTU and the National Bus and Rail Union rejected cost-saving proposals for the third time - although all other grades at the company have now accepted them.
It is not yet known whether the company will proceed to implement the cost reduction measures without union agreement.
If they do, that could trigger an immediate resumption of industrial action, which could potentially spread to Irish Rail and Bus Éireann.
It is thought unlikely that the Labour Relations Commission or the Labour Court will intervene - given that the drivers have already rejected a Labour Court recommendation, a further clarification of the recommendation, and bilateral proposals negotiated directly with management.
It is expected that top management from Dublin Bus will meet Minister for Transport Leo Varadkar in the coming days to discuss the situation.
In July 2012, the Cabinet had to sanction an emergency bailout of €36m for the company.
Dublin Bus originally set a target of August 2012 to complete discussions on cost reduction measures, which it said were critical for the survival of the company - a view endorsed by the Labour Court in its recommendation.
Thirteen months on, no savings have yet been secured.