Ofcom is particularly concerned about "slamming" - where consumers are switched from one supplier to another without their knowledge and consent, usually after a cold-call from the new supplier.Six weeks from today, all fixed-line service providers will be obliged to draw up mandatory Codes of Practice, consistent with published guidelines, and comply with them in all sales and marketing activities, Ofcom announced.The obligation will be reviewed after two years and removed if the regulator finds that sales and marketing abuses have decreased.Ofcom confirmed that it will investigate allegations of mis-selling on a case-by-case basis, and that if companies breach their obligations the regulator may require them to give written undertakings as to their sales and marketing practices.Ofcom has the power to impose fines of up to 10% of turnover in the event of continued breaches.Ofcom Chief Executive Stephen Carter said: "Effective competitive markets need well-informed customers making positive decisions to switch their business from one supplier to another"."These measures should help support progress towards the appropriate levels of clarity and transparency whilst the market continues to mature," he added.