The pressure from shareholders comes following the government's decision to consider legislation that would stop huge payouts to top executives who have failed their companies.
The company has defended the 拢3m pay-off under his three-year renewable contract because of his personal investment in WPP.
However, the Association of British Insurers, representing a fifth of all UK shareholders has said it has "very serious concerns about Mr Sorrell's contract".
Last week, 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.
The government is looking to curb executives pay deals following calls from a number of trade bodies.
Yesterday, secretary of state for trade and industry Patricia Hewitt published a consultation document called 'Rewards for Failure'. She said while the government had no problem with "high levels of reward for high levels of success", however, it was concerned about poor performers who are ousted with "excessive compensation payouts".
Hewitt said the government proposes shorter notice periods, restricted payoffs, and reducing initial job contracts to three years from five.
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