The Communications Authority has fined Safaricom, Airtel and Telkom Sh311 million for not meeting service standards for the 2015/16 financial year.
None of the companies achieved the 80 per cent minimum threshold for the fourth year running. A mobile operator is rated compliant when it attains this mark in the evaluation of key performance indicators.
In a statement on Friday, the authority reported that Safaricom scored 62.5 per cent, while Airtel and Telkom scored 75 per cent each.
But assistant director Rachel Alwala noted they improved from the 62.5 per cent average for the previous period. The industry average is 70 per cent.
Regarding the penalty, she added: "The authority issued the licensees with warning notices for non-compliance and also fined them a sum equivalent to 0.15 per cent of their individual latest financial returns for the period prior to June 30 2017."
Alwala said their report also details comparative performance over the past three years and gives indicators of the companies' performance over time.
Telkom was the best performer with full compliance in four regions - Nairobi, Central, Nyanza and Western.
Airtel came second with full compliance in Nyanza, Western and Nairobi while Safaricom was last with full compliance in Coast and Nyanza.
The authority reported that all three operators failed to meet the call completion target. This refers to the total number of calls that end successfully after being set up.
The target is 95 per cent. Airtel attained 93.3 per cent, Telkom 93.1 per cent and Safaricom 91.8 per cent.
On dropped calls, operators are to achieve rates of less than two per cent.
Telkom was the best performer in this area with 1.5 per cent while Airtel followed with 1.2 per cent. Safaricom did not meet the target with a rating of 2.8 per cent.
CA announced a new quality of service framework for better assessment of compliance by the service providers.
"The new framework will see the authority assess both data and voice services and increase its sampling rates countrywide."
The authority has also initiated measures to enhance its capacity to ensure effective response to emerging technologies and changing consumer service preferences.