Labor has preselected gay rights activist Matthew Loader to take on Industry Minister Christopher Pyne in his Adelaide seat of Sturt.
Mr Loader says his campaign will focus on protecting SA's interests, particularly in relation to shipbuilding and steel manufacturing.
"As I wander around the electorate, I'm hearing that trust is very thin in Christopher Pyne ... (voters) don't seem to have the same confidence that they might once have had that he represents their interests or their values," he told FiveAA radio on Wednesday.
Mr Pyne, who has been the member for Sturt since 1993 and holds a 10 per cent margin, said Mr Loader would be a "serious candidate".
"I'm sure he will put his back into it, as he should," he told FiveAA radio.
"People should have a choice and I welcome him to the contest."
The eastern suburbs seat shapes as one to watch at the July election, with the Nick Xenophon Team performing strongly in early polls.
NXT candidate Matthew Wright, an emergency doctor, has focused his campaign on health, education and climate change.