Sinn Féin is to hold a protest outside Castlederg police station on Friday over what it claimed was "overtly sectarian and brutal treatment of the local nationalist community" by police.
The party's MP for West Tyrone, Pat Doherty, has accused police of helping the Apprentice Boys to flout a Parades Commission ruling, when police allowed a feeder parade from Saturday's Lundy Parade in Derry onto Lurganbuoy Road in Castlederg.
Three men were charged with disorderly behaviour after clashes between nationalist residents and police at Castlefin Park. Three policemen were also hurt.
As the marchers reached the police lines on Saturday, they produced a letter from the commission and were permitted by police to go onto part of the road.
But a spokesman for the Parades Commission said the letter had no legal weight and that the official notification said the march could not go onto Lurganbuoy Road.
But Mr Doherty dismissed the decision of the police as "business as usual" in Castlederg.
"The more things change, the more things stay the same in Castlederg. Never-ending displays of loyalist and unionist triumphalism in this majority nationalist town are accompanied by habitual acts of PSNI aggression" Mr Doherty said.
A police spokesman said the force was "even handed" when dealing with incidents in Castlederg.
Meanwhile, Ulster Unionist assembly member, Derek Hussey has denied claims that marchers paraded in a nationalist area.
He said: "Once again we witness the republican propaganda machine trying to shift blame from their own who undertook the assault on police."