Drivers in the firm are seeking a pay rise of 15% over the next three years.
Dublin Bus has said it cannot exceed an increase of 8.25%, recommended by the Labour Court.
It also said the dispute has cost more than 4m euros (£3.4m) so far, and will leave the firm in a loss-making position by the end of 2016.
The National Bus and Railworkers' Union has said that the action could spread to Bus Éireann and Irish Rail.
In a statement, Dublin Bus said the additional 13 days of planned stoppages in October will cost the company a further 15m euros (£12.9m).
"This will have a catastrophic impact on Dublin Bus's financial position," the company said.
Dublin Bus passengers face disruption until normal services resume on Sunday, with further strike action planned for next week.
Irish Minister for Transport Shane Ross has said his department will not fund pay hikes.
Up to 400,000 commuters in Dublin are facing travel disruption as strikes by Dublin Bus drivers enter a fifth day.