The BBC has learned that hundreds of signatures objecting to the new A5 road between Derry and Aughnacloy have been duplicated.
It's also understood that scores of people have complained that they did not send objecting letters to Roads Service received in their name.
The Department for Regional Development said 'the extent of duplication is difficult to define'.
Around 2000 objections have been lodged.
Thirty letters supporting the road have also been received.
The Mayor of Omagh, Dermott McAleer, said the duplication has damaged the campaign of those opposed to the plan.
"People in general support the road," he said.
"This is a very serious allegation, I support peoples' right to object, but this certainly doesn't help their campaign."
Most objections 'genuine'
The Roads Service said they were 'content that the majority of the objections received are genuine'.
"The way forward is not affected as, in general, the issues raised have been raised across a range of objections received," a Roads Service spokesperson said.
"Roads Service staff, assisted by scheme consultants Mouchel, are currently considering the content of the various submissions.
"Roads Service will treat all correspondence received as a genuine letter unless advised otherwise.
The Alternative A5 Alliance, a campaign group opposed to the new road, said they do not know who is behind the duplication.
Group member and farmer, Derek Donnell, said he's shocked.
"I didn't think that anybody would do that, " he said.
"No one in the Alliance would do that, Roads Service would need to give more clarity on the issue.
"I'm upset that this has happened, it could discredit us.
"We will still fight on."
The Department of Regional Development said a decision regarding the Public Inquiry on the A5 will be made within the next few weeks.