Textiles and fashion, transportation, food and beverages, cosmetics and cleaning items are among them.
The decision is the result of a study conducted last year, which discovered that 40% of green promises made online are false.
“More individuals than ever before are examining the environmental impact of a product before parting with their hard-earned money,” said Andrea Coscelli, Chief Executive of the CMA.
“We are worried that too many businesses are falsely claiming to be environmentally friendly, while true eco-friendly businesses do not receive the attention they deserve.
“The Green Claims Code was created for all enterprises, from fashion giants and grocery networks to small-town shops.
“Any firm that fails to comply with the law risks harming its reputation with customers and may face CMA action.”