A proposal to nearly double the international travel allowance of former MPs has been "slipped in under the radar" according to legal blogger Graeme Edgeler.

Parliament is about to consider boosting the perk for those who were MPs before 1999 by around 80 per cent.

Under the Members of Parliament (Remuneration and Services) Act 2013, the perk is set at around $11,000 a year but National MP and transport minister Simon Bridges wants to increase it to around $20,000 per year.The amendment could be voted on as early as Tuesday and could pass its final reading on Thursday.

Edgeler said the amendment was introduced on Thursday and arrived with little fanfare – and no press release making it impossible for anyone to submit on.

The amendment is going through under the Statutes Amendment Bill and is designed to correct a mistake that saw Air New Zealand inadvertently omitted from the Members of Parliament (Remuneration and Services) Act 2013.

The proposed law change would change the calculation of the maximum rebate on international travel, replacing the cheapest business-class return fare between Auckland and London with the benchmark of an Air New Zealand business-class return fare as at July 1 every year..

Edgeler said for former MPs who qualified for the perk, it would increase the maximum rebate to around $20,000 a year.

Labour MP Annette King said the law change was about correcting the mistake of omitting Air New Zealand and had nothing to do with former MPs "trying to grab something."