Motivational sessions for Marks and Spencer's staff have turned into a van driven recruitment battleground as a shop union tries to woo new Midlands members.
Usdaw has hired the vehicles with ads on to entice employees attending the meetings at the National Exhibition Centre to join up.
A spokeswoman for M&S said Usdaw was entitled to carry out the idea - but the company believed its own in-house forums for staff represented them better than joining a union.
The vans are being driven around the conference complex displaying messages urging M&S staff to join so they can "have an independent voice representing their interests" the union says.
It says staff are listening to American customer service guru Mary Gober deliver a motivational speech in a series of sessions costing £10 million.
M&S say the figures is much lower. "There's a 'nought' less at least," the spokeswoman said.
The M&S spokeswoman said the company had inhouse forums which gave people an opportunity to raise issues. It believed the system worked better than people joining a union.
She said each of the company's 56,000 staff would attend the sessions.
Usdaw general secretary John Hannett said: "We want to work with the company to start rebuilding their strength but their refusal to recognise us means we can't help in that process.
"M&S need to look at their rivals where we are recognised and see the positive work we do."