A union pension adviser opposes the re-election of drug wholesaler McKesson Corp.'s chief executive, citing excessive pay and the failure to heed a shareholder advisory vote to split the chairman and chief executive roles, the Wall Street Journal reported.

In a letter expected to be sent on Monday, CtW Investment Group urged McKesson's shareholders to vote against the re-election of CEO John Hammergren and directors Alton Irby III and Jane Shaw, the business daily said.

Irby and Shaw head the board's compensation and governance committees, respectively.

This is not the first time that CtW, which advises union pension funds, has targeted Hammergren. It successfully campaigned to force Hammergren to resign his board seat at Hewlett-Packard Co earlier this year.

HP's then chairman, Ray Lane, and another director also quit their posts in the shakeup at the No.1 personal computer maker's board in the aftermath of a failed $11 billion deal for Autonomy.

CtW says the funds it advises own a total of 1.4 million McKesson shares out of 228.5 million outstanding, according the Wall Street Journal.

In its letter, CtW opposed the re-election of Irby, the longtime chairman of McKesson's compensation committee, over what it said was "one of the most exorbitant CEO pay practices in the S&P 500", the daily reported.

Hammergren would have been paid $159 million had he voluntarily left the company in March, in what is said to be the largest ever pension benefit for an executive of a public company.

CtW and McKesson could not be immediately reached for comment outside regular business hours.

(Reporting by Chris Peters in Bangalore; editing by Jane Baird)