The information watchdog has launched an investigation into a drive to track down people who are in the country illegally, which was contracted out by the UK Border Agency to private company Capita.
Under the contract - worth £30 million over four years, with a large element of payment by results - Capita contacts individuals by phone, text message, email or letter to warn them that UKBA records suggest they need to leave the country.
Lawyers say some of those contacted are British citizens or have the right to live in the UK. In other cases, the people left the UK several years ago.
The Information Commissioner's Office today said that it had launched an initial inquiry into complaints that UKBA is holding inaccurate and outdated data, in breach of the Data Protection Act.
BBC Radio 4's Today programme reported that the people being pursued are on a list of 174,000 who the authorities have lost track of - mostly overseas workers and students whose visas are believed to have expired. The programme reported claims that the number of people wrongly contacted could run into hundreds, some of whom were receiving several calls or messages a day.
The general secretary of the Immigration Law Practitioners Association, Alison Harvey, told Today: "In theory, this is a group of people who UKBA records show have no right to be in the UK and should leave. In practice, I have seen British citizens getting these messages, I have seen people who have invested £1 million in the UK getting these messages, I have seen nurses getting these messages.
"I have even seen people who left a couple of years ago getting these messages. I have spoken to people who have got in touch (with Capita) and then the texts and phone calls have carried on."
Some British citizens who received the contacts assumed that the authorities would never use text messaging for such important communications and simply regarded them as junk mail and deleted them, she added.
A spokesman for the Information Commissioner's Office said: "It's important that organisations make sure they are taking reasonable steps to ensure they comply with the Data Protection Act, including ensuring the personal information they hold is adequate, accurate, and where necessary, kept up to date.
"We have made initial inquiries as to what steps UKBA has taken to ensure compliance with the Data Protection Act in this instance, and will investigate further before deciding what action, if any, needs to be taken.
"If anyone feels that an organisation has not handled their information fairly then they can make a complaint to the Information Commissioner's Office."
A UKBA spokesman said: "Out of thousands of people contacted by Capita, a small number have been found to have the right to be in the UK or an outstanding application. Anyone contacted in error has been asked to get in touch with Capita to update their records.
"We are mindful of the importance of data protection and are in touch with the Information Commissioner's Office."
A spokeswoman for Capita later said the company had not been contacted by the ICO.