"I don't know what you're talking about," he said, before hanging up.
Laws has three young children with his former wife Leonie Brookhammer and two adult children from a previous marriage. McLachlan has four children.
Last month, Laws announced he was moving his young family to Timaru to take up a development job at Craighead Diocesan School.
McLachlan moved from Wanganui to Dunedin with three of her four children in January.
It is understood she intends to juggle the expanding family with university studies.
At the time of her run for council, McLachlan said Laws had encouraged her bid for public office. "He is my mentor and is helping me. His advice is fantastic. I'm very lucky."
McLachlan is due to give birth in mid-July. She declined to comment.
Laws has said he will take up his new role at Craighead at the end of next month.
Police are continuing to investigate a complaint against him for allegedly smacking a child.