Staff at RSPCA’s Sheffield Animal Centre fear they may be forced to close after travellers moved onto the site's car park.
Diana Radford, operations director at the centre just off Woodbourn Road, said travellers moved onto the site on Sunday afternoon.
She said they had damaged the land by driving a van into a concrete block and forcing it across the car park, ripping up the tarmac.
Ms Radford said: “I am really hoping that we can find a quick and amicable way of moving these guys on and I am praying that it can be sorted because we haven’t got £10,000 for a legal battle.
“Just to give a scale of the task ahead of us, we have go to raise around £100,000 to keep this centre this year – that’s how difficult it is for us.”
Ms Radford said the centre uses the land as an overflow car park and to host outdoor fundraising events such as car boot sales and fairs.
She added that the travellers moved onto the site at around 5.30pm on Sunday and at its height there were 16 caravans parked up.
Ms Radford said: “The business community are really concerned and, unfortunately, we have had lots of phone calls that this community are in the car park.
“I have been down and spoken to them today and I have said it’s causing us a huge amount of problems and people are very upset. They said they were waiting for a caravan that's to be released to them by Derbyshire Police by 6pm and that then they'll be moving on."
Ms Radford said she had also spoken to the travellers about litter on the site and a number of dogs who have been left to freely roam the area.
She added: “It’s distracting us from what we are here to do and we had no water over Christmas so had a massive bill and I’m really worried about this.
“We are going to have to repair the car park but it’s more the amount of money it’s costing us because we are not doing any fundraising and we could have a legal bill of thousands of pounds.”
Stephanie de la Faye, consultant in mental health of Survivors of Depression in Transition, on nearby Jessell Street, said: “It's a very difficult situation and we have to be careful not to tar people with the same brush.
“They haven't caused any issues other than the damage to the car park but for us we have vulnerable women coming to the centre who may feel intimidated by a group of men and dogs hanging outside the entrance.”
For more information on the animal centre or to donate visit www.rspcasheffield.org