The Guardian has stopped star columnist Polly Toynbee writing for a charities and voluntary sector magazine, fearing competition for readers and advertisers.
Guardian editor Alan Rusbridger himself intervened after staffer Toynbee failed to ask permission to write her column for Haymarket charities and voluntary sector weekly, Third Sector, which started last week.
Rusbridger said that the rule was staff should not contribute to titles that compete for readers or advertisers.
According to Third Sector, Toynbee believed the rule was no longer in use since a number of Guardian writers, including staff, wrote for publications that were to some extent competitors.
Among these, Emily Bell, editor-in-chief of Guardian Unlimited, writes a fortnightly column for Broadcast magazine and Guardian assistant editor Michael White contributes on a weekly basis to Health Service Journal.
The Guardian publishes its Society supplement, which includes coverage of the voluntary sector, on Wednesdays, when Third Sector also goes on sale.
Third Sector editor Stephen Cook said: "I'm disappointed, particularly for our readers — people are very defensive about their own territories these days.
We always thought ourselves complementary to The Guardian because as a daily newspaper they can always beat us on news. Also they are more public sector- oriented than we are.
"Third Sector is very Guardian-friendly and a lot of our readers would have a Guardian ethic."
The magazine will now feature guest columnists until a regular one is found.
Copies of the two editions of Third Sector which Toynbee has contributed to will be auctioned on eBay with proceeds going to Toynbee Hall, which works to relieve poverty in East London.