Britain's telecoms regulator said BT, the owner of the biggest fixed-line network, must install business lines more quickly and significantly reduce the wholesale prices it charges rivals for the lines.
Ofcom's demands come less than a month after it said it would impose higher service standards on BT's networks unit Openreach in its review of the communications market.
The new proposals will require BT to install high-speed lines for businesses in 46 working days by the end of March 2017, and 40 working days the following year, down from a current 48 days.
It would also have to reduce prices for the lines, and propose prices and terms for rivals to install their own equipment to use its fiber connections.
(Reporting by Paul Sandle; editing by Sarah Young)