A Sheffield MP has called for an immediate stop to tree-felling works in the city.
Heeley MP Louise Haigh said both parties needed to sit down and negotiate with local residents going forward.
Ms Haigh, who is also shadow policing minister, said South Yorkshire Police has been left in an 'impossible position' and added she was 'deeply uncomfortable' with 'scarce' resources being used in this way.
She also criticised Amey tactics by beefing up private security and the PFI contract the council signed with the provider in 2012.
The council says the trees are either dead, dying, diseased, dangerous or damaging the highway. But campaigners say many healthy trees are being felled for profit.
Clashes on Abbeydale Park Rise and Meersbrook Park Road has seen a number of arrests and people being reported on summons.
Ms Haigh said: “The scenes taking place on the streets of Sheffield are troubling and it is simply untenable for the fellings to continue in this way. One thing is clear, this dispute cannot be solved by ramping up security. That why I believe that the only possible solution is a halt in the fellings and meaningful mediation with local residents going forward.
“Enabling Amey to potentially fell up to 17,500 trees, as revealed through FOI releases relating to the PFI contract, is not at all appropriate and leaves Sheffield at the whim of a private provider.
"I have always believed that PFI contracts in public services put the interests of shareholders not local residents first and that is why I have consistently opposed their use. They are inflexible, anti-democratic & opaque and this contract is no different. The rigid confines of this private contract cannot be allowed to get in the way of a halt in the fellings, meaningful mediation and a negotiated resolution which is now urgent. The needs of the city and local residents must come first.
“As regards the police, their legal duties leave them no choice other than to attend the fellings and to protect the peace, but this has left them in an impossible position. I am deeply uncomfortable with the police’s scarce resource - which have been stretched to breaking point by Tory cuts - being used in this way.”
Sheffield Council has been contacted for a comment.