One of the biggest investors in European companies says it will start voting against boardroom pay plans next year unless firms force executives to hold shares more than three years before cashing them in.

Monday’s warning from Fidelity Worldwide Investment is the latest instance of shareholder agitation over executive pay, sparked by concerns that some top company officials were lining their pockets despite lackluster results and regardless of pay constraint elsewhere in the economy.

Fidelity, which runs assets of around $240 billion, said it had conducted a review of more than 300 of Britain’s largest listed companies and found 238 had either no long-term, share-based pay plans in place or ran schemes that had too short a time frame.

The investment manager said it will vote against company remuneration reports from the start of 2014 if executives are allowed to cash in shares awarded as part of their pay packages within three years.

By 2015 Fidelity expects companies to extend executive shareholding periods to five years or face votes against their remuneration reports at shareholder meetings, the firm said.

Dominic Rossi, Fidelity’s chief investment officer, said the firm wrote to 400 listed companies across Europe last summer asking them to lengthen long-term investment pay schemes.

“We believe that lengthening incentive schemes will change corporate behavior for the better, reducing the temptation to maximize short-term financial performance and instead promote investment and growth,” he said.

Through its mutual funds, Fidelity is among the largest shareholders of many European blue-chip companies.

Career Shares

Rossi has been outspoken on executive pay in recent months and applauded plans by British-based bank Barclays, in which Fidelity is among the 15 largest shareholders, to cut its wage bill as part of a wider shake-up.

Rossi has also suggested in previous letters to executives the introduction of “career” shares which directors must hold until they leave the company.

A run of high-profile challenges in 2012 to executive pay packages by investors frustrated at rising boardroom salaries at a time of declining share prices cost the jobs of some high-profile bosses, such as insurer Aviva Plc chief Andrew Moss, and became dubbed the “shareholder spring.”

Earlier in 2013, Britain’s largest investor associations said they were teaming up to explore ways of giving shareholders a coherent voice in dealings with company boards on strategy, including executive pay.

The National Association of Pension Funds, Association of British Insurers and fund management body the IMA—which speak for funds controlling billions of pounds—said they were acting in response to a government-backed report.

Economist John Kay’s report, commissioned by the U.K. government and published in July 2012, criticized short-termist corporate culture and recommended shareholders are helped to more effectively scrutinize management performance.

In July, a report by the U.K. Parliament’s Business, Innovation and Skills Committee called on the government to push the financial industry harder to adopt Kay’s suggestions.

The report’s authors claimed that “a cultural change will not happen without a catalyst” and that the investment management industry is not implementing voluntary reforms fast enough.