A council says it is facing a possible multi-million pound bill if it fails to complete controversial tree felling work by the end of the year.
Work to replace about 500 trees must be carried out or Sheffield City Council says it will face penalty charges and have to fund the incomplete work.
Councillor Bryan Lodge said the costs "could be into the millions".
He spoke after the council won an injunction to stop campaigners taking direct action to prevent the work.
About 5,500 trees have been felled in Sheffield since the start of a £2.2bn 25-year programme of works, having been assessed as either dangerous, dead, diseased, dying, damaging or discriminatory. They are being replaced with saplings.
However, campaigners claim many of the trees classed as damaging or discriminatory are healthy specimens which should not be cut down.
As a result, regular protests have taken place, many of which have seen campaigners standing inside safety zones erected around the trees in order to prevent the work taking place.
Under the terms of the injunction anyone entering a safety zone will be in contempt of court and face the risk of a fine and possible imprisonment.
Mr Lodge said as a result of the delays the council now needed to "accelerate the work" in order to avoid any financial penalties.
He told BBC Radio Sheffield: "We have a core investment period that ends at the end of this year and we need to get on with [the work] and complete the programme.
"[If we don't] there could be catastrophic financial consequences for the council.
"We wouldn't know what till we reach the end of the core investment period [and can see] the works that haven't been completed that we would then have to fund and penalty charges - it could be in to millions."
Campaign group Sheffield Tree Action Group has yet to announce whether it intends to appeal against the injunction set to come in to place on 22 August.