A Howick and Eastern Bus spokesman said the company had not been notified of strike action.
"I can't comment on anything that may be grounds for the strike, because we don't know about it," he said.
"We're expecting things to be business-as-usual."
An Auckland Transport spokesman likewise said it had not been notified of the strike action.
The strike would be the latest in a long-running dispute between the East Auckland bus company and union members.
First Union has two cases before the Employment Relations Authority alleging breaches of faith by the company. The union is seeking $2 million in penalties.
In March, more than 100 Howick and Eastern bus drivers refused to handle cash for more than a week as part of a strike. They also did not sign on before their rostered shift starts.
Mr Hughes said at the time, drivers had to arrive early for their shifts but it wasn't considered work time.
First Union also accused Howick and Eastern Buses of repeatedly trying to remove weekend and overtime rates.
The March strike also included drivers refusing to drive buses with known safety defects, buses with a defective Hop card reader or ticketing machine, and buses without a working radio telephone or warrant of fitness and road user certificate.
On February 19, Auckland bus drivers went on strike, demanding better pay and work conditions including toilet breaks and break periods between shifts.