BT has been ordered to improve its business services, by installing new high-speed cables and cutting prices, by Ofcom.
The communications regulator said the performance of BT was not "acceptable". And separately, culture minister Ed Vaizey said people signing up for broadband packages may not be charged what he described as an "outdated" line rental fee if they do not use a landline.
The latest orders and recommendations come less than a month after Ofcom ordered BT to open-up its cable networks to rival providers.
Ofcom said Openreach, which is owned by BT, was taking too long to install leased lines and was not doing enough to make sure customers, including thousands of businesses, have their services up-and-running by the date given.
Jonathan Oxley, Ofcom's competition group director, said: "BT is relied on by many companies to install these lines, and its performance has not been acceptable.
"These new rules will mean companies across the UK benefit from faster installations times, greater certainty about installation dates and fast repairs if things go wrong."
Since 2011, the average time between an order for broadband and phone services being placed and the lines being ready to use rose from 40 days to 48 days, Ofcom said. The regulator wants that number reduced to 46 days by March 2017, and back down to 40 days by 2018.
It also wants 80% of lines installed on by the date given to customers, compared with current 75% figures, before rising to 90% in 2018.