David Boyle said there were a number of reasons why members did not contribute.

Only just over half the country's employers say they are paying KiwiSaver contributions for their staff on top of their wages, a Commission for Financial Capability survey shows.

More than half a million KiwiSaver members left $270 million of government contributions unclaimed last year, and the commission said that could be because their workplaces were not upholding their end of the bargain.

To get the full $521 member tax credit each year, members must put $1042 of their own money into their accounts.

Most employed people should be contributing at least 3 per cent of their income and receiving a matching 3 per cent from their employer.

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But a survey in May of 500 companies showed only 55 per cent of employers said they paid the 3 per cent on top of wages, 10 per cent paid it out of their employees' salaries, 20 per cent were not sure, 10 per cent said it varied and 5 per cent offered other pension schemes.

Commission education manager David Boyle said many employers bundled the 3 per cent into an employee's wages, and the employee must choose whether to have it sent to their KiwiSaver account. By law, employers can only include KiwiSaver contributions in salary packages if they have negotiated this with the employee "in good faith".

"If you have two staff on the same wage, and one has the employer's 3 per cent KiwiSaver contribution paid on top and one has it included in their salary, the worker with it included has essentially taken a 3 per cent cut in their take-home pay. It's not surprising if a number of these employees do not contribute to KiwiSaver."

Boyle said there were a number of reasons why members did not contribute – their income might be too low to ​spare anything for KiwiSaver, they may be priortising debt payment, they might be students or not currently in paid work. Contract workers often overlooked negotiation of KiwiSaver contributions as part of their contracts.

"But I think employers need to be more aware of their obligations to their staff. Legislation requires them to pay their 3 per cent on top of wages, and if they want to negotiate to include it in an employee's package, then in good faith they should increase that person's salary by 3 per cent. If an employee thinks their employer is not meeting their legal obligations, they can complain anonymously to IRD."