Barclays has criticised the tactics used by claims management companies regarding payment protection insurance.
Antony Jenkins, chief executive of retail and business banking at Barclays, said: "While claims management companies (CMCs) purport to serve customers by pursuing complaints on their behalf, we fear that many of their practices are causing real harm."
He cited the fact companies were cold-calling customers, collecting personal data and taking advance fees.
He said: "To provide some context, it might be helpful to highlight that in approximately one third of the PPI claims we receive from CMCs, the customer had never had a policy with us.
"These spurious and speculative claims often come at a cost to consumers and give them false hope, while creating delays in addressing genuine cases (including at the Financial Ombudsman Service)."

His comments, sent in a letter to Treasury Select Committee chairman Andrew Tyrie MP in April, were published this week after Natalie Ceeney, chief executive of the Financial Ombudsman Service, gave evidence to the committee.
Ms Ceeney said banks needed to be aware why people chose to go through a CMC.
She said: "The sheer scale of detriment has made PPI a rich opportunity for claims companies to exploit. This has been compounded by a process for getting redress that has seemed confusing and fraught for many consumers- resulting in their feeling unable to 'take on' their bank on their own."
She said her personal worry about CMC was that "consumers are paying for a service they do not need" and that they believed they had no alternative but to use a CMC.
She estimated out of the £9bn paid out in PPI redress, some £2bn could have passed to CMCs.
She said the only solution would be to identify detriment earlier and create wider proactive redress schemes.