Marc Michaels, director of direct and relationship marketing at government communications division the COI, told conference delegates that inclusion on the COI's 2009 DM roster would require agencies and suppliers to have documented green credentials.
The COI is one of the UK's biggest spenders on direct marketing, estimated to be in the region of £35m per year.
"By 2009 you'll need to have clear environmental strategies, policies and processes in place that are properly documented with evidence of success," Michaels said.
Agencies and suppliers would need to think about the materials they propose to use across the course of the project, for instance, ensuring they are from sustainable sources.
In a presentation entitled 'What clients want,' Michaels said that buyers were increasingly choosing agencies and suppliers that reflect a similar environmental position to their own "or even an aspiration they may have".
"Give us what we asked for in the brief but also suggest 'greener' options to us proactively," Michaels told delegates. "Don't assume we will always know the best route. You're the experts. You may know something we don't."
He added that clients "shouldn't insist on eco-credentials unless they have their own house in order".
The COI uses its DM budget to hire direct agencies, mailing houses, data brokers, contact centres, field marketing agencies, postal and door-drop distributors to communicate directly with citizens throughout the UK.
A 32-page report on the 'Profiting from Green DM' conference will be published soon. Email Noelle.mcelhatton@haymarket.com if you want a copy.