It has given them until January 7 to respond and will then consider what action it will take. It is able to impose a maximum penalty of £50,000.
The limit of 3% for the proportion of silent calls to all outbound calls in a 24-hour period was introduced by Ofcom last year after a consumer backlash against the practice, which results in a period of silence on the line before call centre operatives are connected to automated outbound calls.
The two cases could again attract attention to the issue of silent calls, which have slipped off the privacy agenda over the past year.
Ofcom's last intervention was in January, when it issued fines totalling £152,500 to four companies -- Space Kitchens, Bracken Bay Kitchens, Carphone Warehouse and Toucan -- for making an excessive amount of calls.