Unite is planning to hold a national strike ballot for all UPS Parcels workers following a ten month campaign.
Leafleting campaigns have taken place at Camden and the North Feltham trading estate with another demonstration due to take place at the Croydon trading estate later this month.
In a statement, UPS said: “Discussions with UNITE are on-going, and we remain hopeful that a mutually satisfactory agreement can be reached. People are our greatest resource, and UPS works closely with labour unions around the world.
“It is UPS’s policy to comply with all laws governing employment and labour practices worldwide, and UPS is careful to take into account the point-of-view of unions along with the interests of our customers, our employees, our shareholders and our company as a whole.”