The letter, which contains explicit details of an abortion, was slipped under the door of a Hargreaves Street business early on Saturday.

Addressed "especially for you", the letter was unsigned and wrapped in purple tissue paper, adorned with pink and white ribbon.

The store manager, who wished to remain anonymous, said a woman telephoned the business on Saturday afternoon to discuss the contents of the letter with an employee.

He said the woman told the employee that 200 businesses had been earmarked to receive a copy of the letter and that the authors would gauge the success of their campaign before deciding on a residential distribution.

The store manager said the woman revealed her name to the employee, but refused to divulge who wrote the letter and was distributing it.

"I don't think they're going the right way about it at all," the store manager said.

"They made it look like a present and then people open it and don't realise what it is.

"If they clearly wrote on the front `This is regarding abortion and if you have an opinion on this then open it up', then that's fine, but this is like an ambush really," the store owner said.

Earlier this year, the Tell the Truth Coalition distributed pamphlets with shocking images of aborted foetuses to Bendigo homes.

It is unclear whether this group is also behind the latest letter-writing campaign, which appears to be aimed at rallying public opinion against the State Government's plan to decriminalise abortion.

Medicine with Morality founder and Christian Democratic Party member Dr Lachlan Dunjey said he believed the letter was distributed by a small, and perhaps local, group or individual.

"There comes a time where you have to tell what the horrors are and that's always risky.

"But that doesn't negate the fact that this is something that is (shocking).

"Something like that wrapped up in nice pretty pink stuff, you need to be careful where that sort of thing goes."