Three men have been charged with disorderly behaviour following disturbances in Castlederg on Saturday.
There was confusion over the route of a feeder parade
Three police officers were hurt during the trouble which flared as Apprentice Boys returned from Lundy celebrations in Londonderry.
It is understood there was confusion over the route of a feeder parade through the town.
Sinn Fein said police had facilitated a breach of a commission determination, but the DUP said this was not the case.
It is understood the marchers tried to go through a nationalist area.
Parades Commission members consulted with police before the Apprentice Boys were allowed to walk part of the way down the Lurganbuoy Road in the town.
The Sinn Fein assembly member for West Tyrone, Barry McElduff, said the Parades Commission determination had banned the parade from entering the nationalist part of the town.
"Listening to the people on the ground in Castlederg, nationalists are very, very unhappy at the fact that this loyalist parade was able to enter the Lurganbouy Road area of Castlederg," he said.
"Certainly, this is a matter I'll be taking up directly with the Parades Commission and indeed, Irish government minister Dermot Ahern."
However, DUP assembly member Tom Buchanan said he had received a letter stating the commission's ruling that the parade be restricted to last year's route.
"We have went along this particular area for the past number of years and therefore this isn't something that's new," he said.
"The police didn't overturn a Parades Commission's decision, the police implemented a decision that was made by the Parades Commission."
Three men, aged 20, 33 and 28, were charged with disorderly behaviour and other offences and will appear at Strabane Magistrates Court later this month.
Earlier on Saturday, the annual Apprentice Boys parade to mark Lundy's Day in Londonderry passed off without major incident.
However, police officers were atacked by youths throwing stones and bottles at Butcher's Gate.
There were five arrests, but the PSNI said they were generally pleased at how the day had gone.
Originally, 3,500 marchers, including 25 bands, were due to take part in the parade, but numbers were affected due to George Best's funeral in Belfast.
The parade marks the 316th anniversary of the shutting of Derry's gates by 13 young apprentices against the forces of the Catholic King James II in 1688.