People need to be persuaded to speak Welsh, not forced, the first minister has said, after his government was urged to set a better example.
Cymdeithas yr Iaith Gymraeg said just 12% of assembly debate since May 2016 election had been in Welsh.
Carwyn Jones told BBC Radio Cymru he thought a question should be answered in the language it was asked.
He said most voters in his Bridgend seat did not speak Welsh and he needed to communicate directly with them.
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Cymdeithas based its claim on a count of the number of words spoken in Welsh and English during plenary sessions in the main assembly chamber, taken from the official record of proceedings .
It praised Plaid Cymru AM Sian Gwenllian for using the language 99% of the time, and her Plaid colleague Elin Jones - the presiding officer - using it 84% of the time.
Mr Jones - another fluent Welsh speaker - was criticised by the group for using Welsh just 10% of the time.
The campaigners also noted that the use of Welsh by former Plaid Cymru leader Lord Elis-Thomas had dropped from 95% in 2015 to 73 percent since the 2016 election, during which time he quit his party and later became a Welsh Government minister .
Cymdeithas spokesman Osian Rhys said ministers could make "much more use" of the Welsh language.
"It seems to be common practice, or policy, of ministers to make the majority of their speeches in English and to answer English questions in English even though there is simultaneous translation available at all times," he said.
"If the civil service is not providing enough support to prepare speeches and answers in Welsh, there needs to be leadership from the top."
A Welsh Government spokesman said: "Half of Welsh Government Ministers speak Welsh and use it on a regular basis in the chamber and when carrying out government business."