Bill Shorten’s union leader past may be counting against him, with his personal approval slumping and the coalition regaining the lead in the latest Fairfax-Nielsen poll.

The coalition leads the ALP 52-48 on a two-party preferred basis in the poll published on Monday, the first time it has led the opposition in two months.

The gap narrows to 51-49 when second preference votes are taken into account in the poll published on the Sydney Morning Herald’s website.

With Prime Minister Tony Abbott having announced the terms of reference for a royal commission into union corruption, voters may be increasingly wary of the opposition leader’s past as head of the Australian Workers’ Union.

The AWU was one of five unions named by Mr Abbott when announcing the commission last week.

Only 23 per cent of voters oppose the union inquiry and Mr Shorten’s personal approval has slumped by 11 points.

The prime minister now holds a 10-point lead over Mr Shorten as voters’ preferred leader, 49 per cent to 39.

The poll surveyed 1400 electors between Thursday and Saturday.