The Welsh Language Commissioner Meri Huws said she had seen a "significant increase" in complaints about the services offered to Welsh speakers at banks over the past weeks and months.
She said she would use a statutory review to try to find out how improve the experiences of Welsh customers.
She is inviting members of the public to give her feedback.
"As part of the review I will also gather evidence from the banks and experts in the banking sector," the commissioner added.
Welsh language services offered by banks in Wales are to be reviewed by a watchdog