Under Sir Martin's current three-year contract, he would get two years' salary if he was ousted from the company. This is twice the usual amount for directors of UK companies and the deal is being aggressively opposed by shareholder groups.
Shareholders are being urged by the Association of British Insurers and the National Association of Pension Funds to object to Sir Martin's package.
WPP's non-executive directors, led by Bud Morten, chairman of the group's compensation committee, are backing Sir Martin's contract because he has invested around $12m (拢7.2m) of his own money into the company, according to the Sunday Telegraph.
Morten has previously said that Sir Martin's package would be reviewed in August when the board meets to renew his contract.
The pressure from shareholders comes following the UK government's decision earlier this month to consider legislation that would stop huge payouts to top executives who have failed their companies.
Last month, it was revealed that Sir Martin's salary soared 80% to 拢1.6m last year, after he took a bonus of 拢731,000 in the year that the company's pre-tax profits fell 50% to 拢205.5m.
The jump was due to Sir Martin waiving his bonus in 2001, but taking a bonus package of 拢731,000 in the form of shares in 2002. His official salary, before bonuses, is 拢839,000, down by 拢10,000 on last year. The company contributed 拢336,000 in pension payments for him, down by 拢3,000 in 2001.
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