Mr Mark was addressing claims that overseas students were being used as a source of cheap labour in New Zealand.
Mr Scott interrupted him with: "Why don't you just send them back to the countries where they came from? Go back to where you came from. Like you do with all the immigrants - send them home."
Mr Mark said Mr Scott should "button it because he knows there is a petrol station in Masterton right now that has been accused of doing this [using cheap overseas student labour]".
"But he would not know - he does not live there."
The Speaker stepped in, saying Mr Scott's "level of barracking" was unacceptable, and he threatened Mr Scott with expulsion if he interrupted again.
Mr Mark said yesterday he was not yet ready to name the Masterton petrol station of which he spoke.
"I fired that shot at Alastair ... I want to make sure the ducks are in a row."
However, Mr Mark said the petrol station was not alone in its alleged actions.
"It's not an isolated case of someone in Wairarapa acting outside of New Zealand [employment] law."
Asked about his rivalry with Mr Scott, Mr Mark said: "All I know is my office is getting busier ... he is essentially Wellington-based.
"For a guy in Wellington, who serves an electorate reaching up to Waipawa, his travel bill should be huge."
In relation to the Melissa Lee controversy, Mr Mark said: "I haven't done anything wrong and I won't apologise."
Mr Mark said his "standout question" to Ms Lee was something that had been said on another occasion by Prime Minister John Key and National MP Maggie Barry to former Green Party leader Russel Norman - who was born in Australia.
Dr Norman had been told to "go back where he came from", Mr Mark said.
"When a white guy says it to a white Australian ... "
Mr Mark said Ms Lee herself had endorsed plans for a new motorway because it would "keep the criminals from South Auckland" out of the neighbouring district. "So, who's a goddamn racist?"
Mr Mark said he had received enough positive feedback "that I think I'm offering the mainstream view".
In Wairarapa, Mr Mark said he had received "absolutely, outstandingly humbling support from people" and the story was an example of the media being out of touch with the public.
MPs had waited two days before making an issue of his comments and media had "leaped on" the issue, he said.