Openreach, the BT business that deals with the UK's phone and broadband network has been ordered to work harder on repairing faults and installing net access.
UK regulator Ofcom has issued rules that would require the firm to repair faults within two working days.
Customers waiting for a new line to be installed must receive an appointment within 12 working days.
It comes as BT appoints 1,600 new engineers.
BT said the new jobs at Openreach were part of a drive to "improve customer service".
It said it "welcomes the conclusion of this review".
Under the new rules, BT must complete around 80% of fault repairs within one to two working days of being notified and provide an appointment for around 80% of new line installations within 12 working days.
The target will be gradually introduced over three years, Ofcom said.
BT must also publish figures on how its engineers are performing and Ofcom could impose fines if it does not deliver on the new timescales given for repairs and installations.
Elderly and vulnerable
Last year the BBC's Watchdog programme reported that hundreds of people are kept waiting weeks and even months for repairs for line faults.
According to internet service provider TalkTalk a third of faults reported by its customers are not repaired on time.
"Fault repair has not been good enough and we have lots of customer complaints. Elderly and vulnerable people are waiting far too long," a spokeswoman said.
She said that the ISP welcomed the ruling that it had "long campaigned for".
Ofcom told the BBC that the ruling had come as a result of "industry expressing concerns about Openreach's performance".
"The problem was at its worst in 2012. With the exceptionally wet weather, Openreach's performance was at its poorest," said a spokesman.
"Ofcom's proposed new rules over repairs and installations will be met with relief by every household who has ever been left for days, or even weeks, without a working broadband connection," said Dominic Baliszewski, telecoms expert at Broadbandchoices.
"Openreach controls a significant proportion of the UK's broadband infrastructure but has no direct customer relationship, which meant some people were, in effect, stuck in digital limbo if they encountered a service problem their provider was unable to fix."
Sebastien Lahtinen from broadband news site Thinkbroadband added that the ruling could also throw the spotlight on to ISPs.
"Shorter repair times from Openreach may also act to highlight the variations in performance of the retail providers as the clock only starts ticking at the point Openreach are notified of a fault, and sometimes there can be delays with retail providers passing reports to Openreach."
Ofcom's recommendations will now be subject to scrutiny by the European Commission and a final ruling is expected in June.