Labor said Mr Ayres had failed to disclose at least three of the times he had attended GWS games in 2014 and 2015 as member for Penrith, then made his first act as WestConnex Minister the sponsorship of the club, for an undisclosed sum.

It is common for MPs to accept corporate hospitality at sports events, but it must be reported under pecuniary interest disclosure rules.

Opposition Leader Luke Foley said the problem was not only Mr Ayres' failure to disclose the three occasions, but the subsequent bestowal of a sponsorship to the same club under Mr Ayres' WestConnex portfolio.

"This is classic snout-in-the-trough Liberal behaviour," Mr Foley said. "A minister, nosebag on, first in line at a corporate function, and giving every indication of rewarding his hosts with taxpayer money.

"This sponsorship stinks. What we're left with is a massive exercise in taxpayer-funded Liberal Party propaganda."

Mr Ayres announced earlier this month that the Sydney Motorway Corporation, the publicly funded body responsible for the controversial $17 billion WestConnex motorway, would sponsor the GWS Giants in a three-year naming rights deal.

He refused to disclose how much the GWS Giants sponsorship is costing taxpayers.

Mr Foley also pointed out that the chairman of GWS Giants is former Business Council head Tony Shepherd, who was also the chair of the WestConnex Delivery Authority until September 2015.

Mr Ayres has been the Sports Minister since April 2015, and was made Minister for Western Sydney and WestConnex by Ms Berejiklian in January.

Mr Ayres did not address the conflict of interest claims. He said: "As the Sports Minister for NSW, I regularly attend sporting events."

The GWS Giants chief executive David Matthews said there was no connection between Mr Ayres' acceptance of corporate hospitality and the sponsorship, and defended having politicians attending sporting events.

"Having a western Sydney business investing back into western Sydney community programs I think is outstanding," he said. "They are doing similar things with Wests Tigers.

"The relationship between the Giants and WestConnex in relation to community development programs was developed and finalised well before Mr Ayres became the responsible minister."

A spokeswoman for the Sydney Motorway Corporation said: "Critics of our partnership want to deny western Sydney people access to services and programs that bring them together, improve their health outcomes and set them up for a brighter future."

She declined to disclose the value of the sponsorship, saying it was commercial in confidence.