By Reuters Staff 2 Min Read TOKYO, Dec 17 (Reuters) - Japan’s anti-trust watchdog said on Thursday it had issued a warning to advertising giant Dentsu Group over its action to pressure subcontractors not to work with a rival company. The Japan Fair Trade Commission (JFTC) said it had found that a Dentsu employee had in May told subcontractors the company would stop dealing with them if they worked for the rival on a novel coronavirus aid programme. Dentsu used “improper means” with the subcontractors, although the action was not found to have been a violation of anti-competition rules, Koji Mukai, a senior JFTC official in charge of the investigation, told reporters.