Hundreds of police officers from across Britain who were deployed in Northern Ireland for the G8 Summit will return on Wednesday for the Twelfth.
PSNI Chief Constable Matt Baggott has drafted in 630 extra officers - 30 units of mutual aid - to help the PSNI manage this year's 12 July Orange Order parades.
He said this year represented a "unique 12 July" with about 550 parades taking place, of which 43 were regarded as "sensitive".
Northern Ireland's political leaders have warned against street violence and illegal protests.
Mr Baggott said only officers who had been trained for the G8 Summit would be used, and they would be sent to police the "less-sensitive" areas.
"This is not going to be the routine but it was important, as we see the depth and scale of the parades on the 12 July, that we are prepared for every eventuality but most importantly we support people in parading and keeping people safe," he said on Tuesday evening.
But Steve Williams, chairman of the Police Federation of England and Wales, said the deployment of mainland UK police officers to Ulster was alarming.
He said: “Whilst we will always endeavour to support our colleagues in Northern Ireland to the best of our abilities, this request raises the alarm on many fronts.
"Mutual aid deployment to the G8 Summit was a resounding success and the work that went into this in the lead up to and during cannot be underestimated.
"This event was a milestone in the history of British Policing and an intended one-off. No discussions have taken place to set this as a precedent for an on-going arrangement should the need arise.
“Deployment of police officers from England and Wales to Northern Ireland for the forthcoming marching season clearly demonstrates resourcing issues within the Police Service of Northern Ireland.
"We have concerns in terms of the health, safety, training and protection of those deployed. Let’s not forget the resulting resilience issues for those left policing the home counties.
"Mutual aid to Northern Ireland cannot be provided on an ad hoc basis, given the preparation required to police a potentially volatile environment.
“The budget for counter terrorism was protected in the 2015/16 CSR. What the government has failed to recognise is that every officer in the country plays a role in combatting terrorism yet our numbers are diminished, leaving forces desperately seeking mutual aid in times of need. This is not right. We should have a police service that is fully resourced and fit for purpose.
“We ask that there is a full consultation process about the proposition of further mutual aid to Northern Ireland.”
A joint statement was issued by Northern Ireland's five party leaders on Tuesday evening which appealed for peace and stated they do not want anything to undermine the positive image of Northern Ireland seen during the G8 Summit.
It said: “We appeal to community leaders and, indeed others, such as parents to seek a peaceful parading season to avoid an impact on our citizens, through damaged community relations or the life-restricting consequences of criminal records.”
“We are committed to building a positive image of Northern Ireland seen as a result of the G8 Summit, through the UK City of Culture and, hopefully, the forthcoming World Police and Fire Games and All Ireland Fleadh. We do not want to see anything which undermines the good work already done by so many.”
“For those who wish to see a different approach to decisions around parading we point you to the fact that the Executive has agreed to all-party talks commencing later this year. This will look at parading and other contentious issues. That is the forum through which we need to consider the future of parading decisions not through illegal protests or other unlawful action on the streets.”