Bedfordshire Police said a man in his 30s remained on bail while inquiries continued.
Unite says workers – primarily based at the depot in Dunstable Road – are dissatisfied with responses to the complaints and feel those affected have not been not adequately supported.
The union says reports from staff include unwanted physical contact, touching, as well as inappropriate gestures and sexually explicit remarks.
Bus services in Luton and the surrounding area could be disrupted, a Unite spokesperson said.
Unite general secretary Sharon Graham said the shop steward – who was “fired for speaking out” – must be reinstated.
Although, Arriva said it was “wholly inaccurate” to suggest the employee was dismissed for their involvement in raising “what is now a police matter”.
Unite regional officer Jeff Hodge said responsibility for any disruption lay with Arriva and called for the dispute to be resolved.
A spokesperson for the bus company said: “Arriva takes matters of this nature extremely seriously, and employees are encouraged to raise any concerns through the avenues provided.
“Should any situations arise, appropriate management intervention is deployed, and support is offered and provided to employees.”
They continued: “Arriva remains committed to resolving this dispute and will work to minimise any impact on our customers or bus services.”
