BT has been accused of profiteering from nuisance calls by an MP who leads a parliamentary group to tackle the problem.
The cross-party parliamentary group on nuisance calls claims services to tackle the problem should be free of charge, after BT introduced a fee for its caller ID display system.
BT said the service would be free for customers who signed up to a year-long contract, allowing them to screen calls from marketing tele-operators, but it would cost others £1.75 a month.
But Liberal Democrat MP Mike Crockart told the BBC: "When we started to look into this, BT talked about how important it was to have caller ID, but failed to mention that they were about to start charging for it.
"This can be seen as profiteering on the back of nuisance calls."
The telecoms firm said in a statement that it takes nuisance calls very seriously, a spokeswoman adding: "We work with Ofcom, industry and consumer groups to tackle the problem.
"BT is improving the network over the next 12 months, so that the caller display service will also be able to display full telephone numbers calling from abroad."