Print Week reports that Unite has sent notice to Trinity Mirror that print workers employed by the company will begin "working to rule" from 19 September.
Unite members have voted to take industrial action short of a strike, in response to a nationwide pay freeze imposed by Trinity Mirror last November.
They have opted to "work to rule", which will include working to exact hours and guidelines set by the company.
Unite national officer Steve Sibbald told Print Week: "We will continue indefinitely until we get a response from the company."
The two parties will continue with negotiations in the hope of reaching a solution before any action takes place.
Via Tom McGowran