Drivers at Bus Éireann and Dublin Bus could agree to future strikes today.
SIPTU members in each company are meeting this morning to consider a ballot for strike action, after talks on Government plans to privatise 10% of public bus services broke down yesterday.
Unions say the National Transport Authority (NTA) has threatened to privatise routes without agreement from unions.
SIPTU and the National Bus and Railworkers Union want guarantees on their members' conditions if the privatisation goes ahead.
Willie Noone of SIPTU says bus workers need assurances that their employment rights will be upheld.
"There is legislation in place protecting pay and conditions of employment - we don't believe that legislation is strong enough, we want it strengthened," he said.
"What we do want is we do want, at least at the minimum, that that legislation that is currently in place would be ordered and enforced, and penalties taken against employers who don't adhere to the current legislation".
"And at the moment, we're not getting any guarantees on that."