The code, which is voluntary at present, covers activities such as house-to-house collection of goods and the operation of recycling banks. It was introduced in 2005 to promote best practice.
Lekha Klouda, director of the association, said: "By moving to a mandatory code in 2008 we are making clear the importance the sector places on maintaining and improving standards."
Ken Blair, chief executive of British Heart Foundation Shops, said: "This will strengthen the sector."
Megan Pacey, director of policy and campaigns at the Institute of Fundraising, said: "In future there may be an institute requirement for something that covers trade and retail more generally that isn't done through charity shops."