Senedd members warned a shortage of teachers could undermine a target to reach a million Welsh speakers and double daily use of the language by 2050.
Eluned Morgan, giving a statement on the Welsh education bill on 16 July, said the bill will give every child in Wales a fair chance of becoming Welsh speakers.
She told members that the bill would put the vision of a million Welsh speakers on a statutory footing.
But opposition parties warned the success of the bill will hinge on the teaching workforce.
Tom Giffard raised concerns about the recruitment and retention of Welsh-language teachers, questioning if the workforce is adequately prepared to meet the challenge.
The Conservatives’ shadow Welsh language secretary said teachers who teach through the medium of Welsh are, on average, older than their counterparts.
He warned the bill will add to the workload of teachers who are already grappling with a new curriculum and additional learning needs reforms.
He supported moving away from the “blunt instrument” of “fluent” or “non-fluent” to the Common European Framework of Reference for Languages.
But cautioned against “lowering the bar” to count people towards the target of a million Welsh speakers set out in the Cymraeg 2050 strategy.