Guide dog owners are calling for stronger penalties for cab drivers who refuse to carry them.
The charity Guide Dogs claims owners are being let down because the penalties issued to taxi and minicab drivers who flout the law and refuse to take assistance dogs are inadequate.
Despite illegal access refusals causing distress, the fines for drivers who refuse are no higher than those given to people who dodge train fares or evade TV licences, it says.
New research from the charity found that prosecutions were rare.
Even when fines are handed out, they are low, with some licensing authorities that responded reporting fines as low as £50 to £100.
In a bid to change the law, more than 100 guide dog owners will visit Parliament on Wednesday to call for tougher sentences for taxi and minicab drivers who turn away assistance dog owners.
James White, senior campaigns manager at Guide Dogs, said: "Imagine you were turned away by a driver. This happens to people living with sight loss with shocking regularity just because they are accompanied by a guide dog.
"It's not only illegal, it knocks people's confidence and stops them doing the everyday things that most people take for granted.
"We want tougher sentences for drivers who turn away assistance dog owners.
"We would also like to see the introduction of disability awareness training for all taxi and minicab drivers across Britain."