At the moment, calves and lambs can be on board a vehicle for 21 hours without a break. For adult animals, it's even longer.
But the rules are often broken.
The RSPCA wants there to be an eight-hour journey limit, with longer rest breaks.
It is also calling for better conditions on board the lorries.
Disregard for animal welfare
An RSPCA spokeswoman said: "Our undercover officers have witnessed blatant disregard for transport laws and the welfare of animals.
"What is the point of moving livestock, often across several countries, just to slaughter them at the end of the journey?"
Some countries say they prefer to slaughter the animals themselves because they have different ways of preparing the meat.