Members of the UVF have been accused of stealing sandbags and selling them to residents in east Belfast worried about their homes being flooded.
A major multi-agency operation got under way on Thursday to prepare residential and industrial districts on both sides of the River Lagan that were identified as being at major risk from flood waters.
Walls of sandbags were built up in Sydenham in east Belfast and on land around the docks on the opposite side of the Lagan.
Police had to guard sandbags in some areas after reports they were being removed.
More than 500 sandbags lining the Connswater River had to be replaced after they were stolen, and sandbags protecting the pumping station were also purloined.
A senior source within one of the bodies involved in distributing the bags said he was informed individuals from the UVF were involved.
The situation was discussed during early-morning meetings between relevant agencies, he said.
There were reports of the stolen sandbags being sold in areas of east Belfast yesterday morning for £1.50 each.
PSNI Assistant Chief Constable Stephen Martin said: "I've heard lots of reports of sandbags being removed that have been put in place to protect people.
"If people have been taking property like that and trying to make a profit I think it is morally reprehensible.
"I think they are damaging their own community, and if anyone has evidence of that we will certainly look to establish whether a criminal act has taken place." Former Lord Mayor of Belfast Gavin Robinson, a DUP councillor in the east of the city, said he was saddened by reports of the theft of sandbags.
"At a time when people are stretching themselves to help others, reports of sandbags being stolen and sold are disturbing and depressing," he tweeted.
Police appealed to people to leave sandbags where they had been positioned, as with more weather warnings in place in the coming days, they would be needed to hold back flooding.
"Police are again urging residents to not remove sandbags which have been placed at key points to protect the entire area," a spokeswoman said.