Subir Raha, who was last week denied an extension as head of ONGC on the basis of a critical performance appraisal by former petroleum secretary S C Tripathi, had hit out at the latter for passing "invalid, prejudicided and illegal" orders.On May 23, his penultimate day in office, Raha had written to Petroleum Minister Murli Deora saying Tripathi, during his tenure that ended on December 31, 2005, "authorised several illegal and biased actions."Tripathi pushed for appointment of two additional government directors, on top of three already present, on the ONGC board in violation of "listing agreement/corporate governance" and insisted on nominating DGH, the sector regulator, on the board in "unquestionable conflict of interest," Raha said.Sources said Raha's letter alleged "intimidation" by Tripathi "to comply with these orders, especially the nomination of the DGH". It said Tripathi "threatened" to remove Raha as chairman and managing director of ONGC by "voting in the AGM on the strength of majority in equity."Raha, who is reported to be suffering from obstructive jaundice and is to undergo surgery in a day-or-two, did not take calls for comments.Contrary to popular perception, it was Tripathi who had refused to sign the performance MoU with ONGC, Raha's letter said, adding the former secretary "propagated" the canard that resources were being diverted from the company's core exploration and production to downstream petrochemical and power projects.Tripathi, the letter said, persistently denigrated ONGC and especially its CMD in meetings and on file.