Woolworths has withdrawn a line of cheese from sale after a customer found a safety pin in the middle of a block of cheddar.

Former school teacher Patrick McMullen from Orange in New South Wales says he cut off a thick slice from a 500-gram block of Woolworths home brand cheddar cheese on Wednesday night, and when he began chewing it, he felt something strange in his mouth.

"So when I discharged that from my mouth out came a safety pin that had been in the cheese," he told the ABC.

"I cut a reasonably thick slice, put it into my mouth, I had no idea. At first I thought I'd broken a tooth because I felt something hard in my mouth ... [but] it turned out to be a safety pin.

"It was a shock. I rang the Woolworths hotline and they assured me that they take this sort of matter seriously and that someone would ring me at 9:00am, which they did.

"Since then I spent most of yesterday negotiating on the phone with a spokesperson from Woolworths about how prevalent this may or may not be, and that if they couldn't give me any assurance whether it was a one-off or not, I pressured them to withdraw the product from all Woolworths [stores] in Australia."

A Woolworths spokesman has told the ABC a customer "did present to Woolworths yesterday with a complaint about a foreign object in a block of cheese".

"Woolworths immediately withdrew the product from sale," the spokesman said.

"Woolworths is continuing to investigate the issue and has been in touch with the customer a number of times and will talk to him again today."

A spokesperson for Devondale Murray Goulburn (MG) said the company takes safety matters "very seriously" and the incident is being investigated.

"MG has very stringent food safety processes in place throughout our supply chain," the spokesperson said.

"Metal detection and X-ray units are a critical point within our manufacturing process and are tested regularly for accuracy.

"The investigation into this incident is still underway, and we'll be keeping the customer and Woolworths up-to-date as it progresses, and until we have finalised this important process."

Mr McMullen says he felt compelled to share the story with the media because he wants to ensure there are no other contaminated products in supermarkets across Australia.

"I was a school teacher for 30 years and I spent my whole life caring for children and one of my greatest concerns is that a child could easily choke on this sort of thing," he said.

"I'm not a trouble maker, my concern is for the safety of everyone."

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