Prime Minister John Key has indicated National will campaign on further changes to labour laws - and will not rule out reinstating a youth minimum wage or changes to collective bargaining.

At the Seafood Industry Council conference yesterday, Mr Key said making the labour market more flexible was a priority as the economy began to grow and National intended to unveil further changes in the election campaign.

Asked later about the changes, he said it was too early to reveal details.

"We're not talking dramatic changes but we are likely to campaign on some changes."

He would not rule out a return to a youth minimum wage - advocated by business groups as a way to reduce youth unemployment - or changes to collective bargaining. However, he said a further extension of the 90-day period was unlikely.

National's 2008 policy included allowing workers to bargain collectively without belonging to a union - a provision strongly opposed by the union movement and which National has not yet taken action on.

When asked if the new policies would please the union movement, he said he doubted any labour law changes would.

"[The changes] are about making sure there is balance and fairness in the employment environment. We know flexibility in the labour market is hugely important in terms of encouraging employers to take on employees, we also recognise we need to balance the rights and safety of employees."

Mr Key's comments coincided with figures showing numbers on the unemployment benefit dropped by 3000 in the last year and more than 9000 people went off benefits into work in May. He said the 90-day period meant employers were keener to take on new workers and that had helped keep employment rates lower than they would otherwise have been.

However, unions and Opposition politicians were sceptical about Mr Key's proposed changes.

Council of Trade Unions secretary Peter Conway said National had already eroded workers' rights, including restricting union access to workplaces and allowing a week's annual leave to be traded in for cash.

Despite Mr Key's claims, since the 90-day probationary period began youth employment had risen from 17.9 per cent to 27.5 per cent.

Labour's spokeswoman on labour issues, Darien Fenton, said National was disparaging of workers' roles in the workplace.

"Productivity increases and health and safety improvements require the active involvement of workers. If the Government doesn't get that, then we are doomed to be a long-hours, low-wage, low-skill economy."