BT customers are complaining about changes that will mean they lose access to two Sky Sports channels.
In August, BT will launch two of its own sports channels, which it will offer free to its broadband customers.
BT Sport will take over slots currently occupied by Sky Sports 1 and 2, so BT is planning to deliver them via its Infinity fibre-based broadband service.
But a "very small proportion" of customers with slower broadband speeds will lose the channels, BT has said.
BT has written to customers offering an upgrade to Infinity in areas where it is available. Even if this involves equipment changes or additional wiring BT has said this will not mean extra costs for customers.
Many have taken to forums on the BT support site to complain.
For those outside these areas, BT has developed a separate technology that will stream the Sky channels over copper cables as long as they support a minimum line speed of 5.2Mbps.
A BT spokesman said some of its customers, believed to be about 15,000 people, who did not have a fast enough copper connection to support the lower speed streaming system, would lose access to both the Sky channels.
In compensation, he added, they would be offered six months' free broadband.