A company employee has been sacked after she tried to get her own back on a colleague – by putting laxatives in chocolate brownies she baked for the send-off.

There may have been tension between the 47-year-old woman and her departing colleague, police said.

No one ate the brownies and the cook has not been charged, but officers in the US state of Michigan said the matter would have been different had someone consumed the chocolate treats.

Managers at the engineering firm where she worked confiscated the brownies after another staff member tipped them off.

The suspect initially denied adding laxatives, but after police told her investigators would test them for tampering, she admitted she had done so, the Ann Arbor News reported.

Saline police chief Jerrod Hart said the incident was something schoolchildren should normally be reminded of - that tampering with food is not a joke, especially as allergies and medical concerns may not be known.

"A lot of times you see it in movies or TV shows where someone tries to do this or play a joke, but it's very serious," he said. "It's a criminal act."