TimePlan's jibe against bitter rival Select came after the latter launched a complaint about TimePlan's claim, in adverts, to be "the UK's largest teacher-recruitment specialist".
As The TES reported in March, Select complained to the Advertising Standards Authority claiming it was larger, on several different measures, than its rival.
Last week, TimePlan was asked to change its adverts, which have featured in The TES. It had already done so by the time the complaint was upheld. However, TimePlan's managing director, Tish Seabourne, this week hit back. Their rival's bitterness, she said, stemmed from Timeplan's rejection of a takeover bid three years ago.
She said: "TimePlan is a specialist company whose only customers are teachers and schools. It is regrettable that the ASA decision means we can no longer make this distinction between ourselves and large multinational agencies such as Select, which supplies truck drivers, plumbers and refuse collectors."
TimePlan points out that Select Education, the company's recruitment arm, is just a small part of the world's third-largest high street recruitment company, a multinational supplying a bewildering array of professionals. But Select says that its teacher-recruitment business is completely separate.
Chief executive Bob Wicks said: "Although it's part of a large group, Select Education deals with nothing other than education."