* Fujitsu shares down 4.3 pct, biggest loser in the Nikkei
* Fujitsu changes reason for ex-president Nozoe's resignation
* Fujitsu: Nozoe link to firm with "unfavourable reputation"
* Nozoe, through lawyer, has contested Fujitsu claims
* TSE: looking into Fujitsu's disclosure on issue (Adds TSE comments)
By Taiga Uranaka
TOKYO, March 8 (Reuters) - Shares of Fujitsu Ltd, Japan's largest IT services firm, fell more than 4 percent on Monday amid a dispute with former president Kuniaki Nozoe over the circumstances that led to his abrupt resignation last year.
The Tokyo Stock Exchange said it was checking with Fujitsu on why it changed the reason for Nozoe's resignation, announced in September after he had spent just 15 months in the top post.
Fujitsu said on Saturday it had now dismissed Nozoe as an adviser and that the main reason for him stepping down as president was not illness, as it stated at the time, but his association with a firm whose group was said to have an "unfavourable reputation".
Nozoe, through lawyer Kei Hata, has contested Fujitsu's claims and sought to have his resignation nullified to "restore his honour", saying he was forced out for false reasons. Hata told Reuters his investigation did not find the company in question to have improper links.
Nozoe could not be reached for comment.
The tussle between Nozoe and Fujitsu management threatens to disrupt the firm at a time it is rushing to cut deals and restructure to keep pace with global rivals in the computer services sector, and could invite scrutiny over its disclosure.
"Investors fear management disputes like this may slow down restructuring efforts," said Yumi Nishimura, deputy general manager of investment strategy at Daiwa Securities Capital Markets.
But she and others said the impact of the public standoff between Nozoe and Fujitsu would be limited unless it escalates.
"It's not good for Fujitsu's image, but it's not as if it's the current management that has been hit by scandal," said Naoki Fujiwara, a fund manager at Shinkin Asset Management. "I don't see a big impact on its earnings."
TSE spokesman Kazuhiko Yoshimatsu said it was still unclear if the exchange would take any punitive action.
Fujitsu says the problem stems from a project Nozoe was working on around February 2009 that involved an outside company whose representative director was a long-time acquaintance.
Fujitsu said it discovered that the company was part of a group that had an "unfavourable reputation" and conducted an investigation. It said it determined that dealings with the company would be inappropriate and that Nozoe agreed.
However, Nozoe continued to have relations with the company, Fujitsu said in the statement, without elaborating on the nature of that relationship. At the same time Fujitsu said Nozoe had not committed any illegal acts.
Fujitsu shares fell 4.3 percent to 559 yen by midday, the biggest percentage loser among Nikkei 225 average components. The benchmark gained 1.7 percent on strong U.S. jobs data. (Reporting by Taiga Uranaka; Editing by Edwina Gibbs and Michael Watson)