The take-up of Welsh language services run by large businesses and public bodies can be as low as 1%, a snapshot survey for BBC Wales suggests.
The assembly government wants to legislate on new language rights
The Dragon's Eye programme found at the Principality building society only 1% of mortgage customers requested correspondence in Welsh.
The Welsh Assembly Government said Welsh-speakers were not aware of the services that were on offer.
The CBI in Wales has said the debate was "driven by politics" not customers.
BBC Wales' Dragon's Eye programme contacted 10 Welsh businesses and public bodies to take a snapshot of the current usage of Welsh language services.
It found that at the Principality building society only 1% of mortgage customers requested correspondence through the medium of Welsh.
Barclays reported that only 0.25% of its Welsh customers were registered with its dedicated Welsh language telephony service.
CALLS IN MEDIUM OF WELSH
Cardiff Council: 1.2%
Welsh Water (2007-8): 9.2%
Department of Work and Pensions: 1 Welsh language call for every 135 in English
British Gas said fewer than 1% of its Welsh customer base currently received billing communication in Welsh.
Welsh Water said demand for its Welsh language call centre rose by 50% after an advertising campaign.
It received around 9% of its calls through the medium of Welsh in the wake of the campaign for its Welsh language call centre.
However, the assembly government said utility customers were always aware what Welsh language services were available.
Meanwhile, the Welsh assembly's own website reported visitors were almost 30 times more likely to visit the site via its English domain name assemblywales.org than its Welsh domain name, cynulliad.org.
At Cardiff Council, 1.2% of calls to the Connect to Cardiff council helpline were in Welsh.
David Rosser, director of CBI Wales, said: "One of the big problems in this debate is that it's driven by politics not by customers and users.
"The companies that already provide a variety of services to customers in the Welsh language get a dreadfully low take up."
But the Welsh Language Society, Cymdeithas yr Iaith, said the findings reflected "random and unreliable" services offered in the private sector.
The society's campaign officer Sioned Haf said: "Very often these companies have only one Welsh speaker in their offices to answer your call.
"If that person is away, or does not have a speciality in your field of enquiry, then you do not have a viable Welsh language service."
The Labour-Plaid coalition had asked for the right to legislate - known as a Legislative Competence Order (LCO) - on Welsh Language legislation in the spring.
This could give Welsh speakers more rights to access services in Welsh. It is thought discussions are to commence at cabinet level shortly.
The power-sharing agreement between the two parties sets out an intention to "confirm official status for both Welsh and English, linguistic rights in the provision of services and the establishment of the post of language commissioner".
It is not clear what, if any, demands will be made on the private sector.
Dragon's Eye is on BBC2W at 2100 GMT and on BBC 1 Wales at 2235 GMT.