Premier Transport Group, a company owned by known Liberal donors, has provided two buses to Mr Constance's campaign to win the Labor-held marginal seat of Gilmore.

Daily bus quotes show the running cost of the buses, which show Mr Constance's face as part of his federal tilt, would likely cost in excess of $188,000.

The buses have been touring the NSW South Coast electorate since mid-February and advertising on a coach typically costs roughly $800 each day, at commercial rates.

With the election on May 21, that is around 95 days of usage.

Both buses are registered to Premier Transport Group, which during Mr Constance's time as transport minister, received $56 million in contracts from the state government.

This includes a $20 million contract for outer metropolitan bus services and another $39.9 million for regional charter service.

The Illawarra Mercury in 2019 revealed Premier Transport was contracted to run trial regional on-demand bus services that was costing taxpayers $40 a trip.

The bus company is owned by brothers Gerard and John King who, according to the NSW electoral commission, have donated $22,785 to the Liberal and Nationals.

Mr Gerard King was also seen campaigning with Mr Constance on April 5, spruiking electric buses in the Shoalhaven region.

Australian Community Media contacted Mr Constance's office, which confirmed the money was coming from the Liberal Party and would be disclosed in accordance with the Australian Electoral Commission's donor returns.

"This advertising has been paid for by the Liberal Party campaign, which will be declared along with the other Liberal Party campaign expenditure to the Australian Electoral Commission in line with our obligations under the Commonwealth Electoral Act," a Liberal party spokesman said.

It is also not known if a quid pro quo negotiation for the buses contract was entered between the Liberal party and Premier Transport.

Premier Transport was also contacted for comment over the cost paid for the buses.

The company used to trade under the name of Bus & Coach Industrial Association (NSW), which appears on the NSWEC donor disclosure.

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Labor's Fiona Phillips currently holds the seat on a margin of 2.6 per cent.

Mr Constance was heavily backed by Scott Morrison to contest the seat, despite condemning the Prime Minister during the Black Summer bushfires.

In January 2020, after locals shouted abuse at Mr Morrison in the streets of Cobargo, NSW, the then transport minister said locals in his Bega electorate had given the PM "the welcome he deserved" and criticised his lack of leadership.

It was a different story during the election campaign, when the two men addressed the earlier tension with words of praise for each other and Mr Morrison said he didn't hold Mr Constance's comments against him.

"I love it that he's on my team because he calls it and he calls it straight. And he did on that day," Mr Morrison said.

Mr Morrison has visited the seat of Gilmore twice during the election.