Companies taking sand from the bed of Lough Neagh have been told to stop or face prosecution.
The environment minister issued enforcement notices to five companies telling them to cease activities by the end of next month.
Mark H Durkan said a “detailed investigation” had convinced him the firms were flouting an earlier instruction to stop dredging.
Failure to comply with the enforcement order is a criminal offence.
Sand has been extracted from the lough since the 1930s, but the operation has never had permission.