Unite's appointment of Tangent One comes in the same week that the , which led Barack Obama's online election fundraising campaign, to create a campaign against the part-privatisation of the Royal Mail.
, which highlights an online petition and the ability to show support for Unite on Twitter, Facebook and other online destinations. The campaign will also span email and direct mail.
The petition focuses on fighting BMW's recent decision to lay off 850 agency workers at its Mini production plant in Cowley with minimal notice and pressuring the manufacturer to enter into negotiations with its employees and Unite over the future of the plant.
Unite, which has more than 2m members, said it is focusing on longer-term digital activity aimed at channelling support for a national strategy for manufacturing.
Greg Jackson, chief executive at Tangent One, said: "We are delighted to be working with Unite to help them develop their organisational capacity to campaign online as effectively as they do offline.
"To devise a campaign, design it, develop it, get sign-off and then email thousands of union members -- all within 24 hours -- is an incredible achievement by the teams here and at Unite."
Tangent One is part of Tangent Communications group, which employs more than 140 people and has an annual turnover of more than £17m.