IBM staff in the UK have called for the IT giant to introduce a more transparent pay system.

The employees, who are members of the trade union Unite, have branded the current system as "highly secretive". The union claims that IBM is refusing to share with it the details of its pay system to demonstrate that it is free of discrimination.

"Unite has been seeking answers to how IBM intends to ensure that its highly secretive pay system stops staff being the subject of discrimination and continued unfairness in the workplace," said Kevin O'Gallagher, Unite national officer.

"To date, the company has ignored all reasonable approaches, but Unite intends to hold the company to account."

IBM, which turned 100 this week, refused to comment on Unite's accusations, beyond saying: "IBM has and continues to respect the legal rights of its employees to join, or refrain from joining worker organisations, including labour organisations or trade unions.

"The company's long-standing belief is that the interests of IBM and its employees are best served through a favourable, collaborative work environment with direct communication between employees and management."

A recent survey by PayScale compared the pay at nine major IT employers in the US, including IBM, HP, Microsoft, Facebook and Google. It found that Google employees earned the highest salaries in the tech industry, with a starting salary of $82,600 and a mid-career median pay of $141,000.

In comparison, IBM pays a starting salary of $65,100 and a mid-career median pay of $107,000, coming in the bottom four. IBM was also found to have employees with the highest median age, of 44, with one of the lowest percentages of female employees (24 percent).

However, IBM's employees were also the most loyal, serving a median tenure of eight years, just slightly ahead of HP's seven years. In addition, IBM staff had the longest holidays, at 3.2 weeks a year.