Peers will vote on Monday on a government move that could delay action on children’s access to social media for up to three years, which has triggered a backlash from campaigners and senior figures in the Lords.

Ministers tabled an amendment to the children’s wellbeing and schools bill that would allow them to wait before introducing new restrictions, Critics warn it risks watering down earlier commitments to act within months and could result in only limited interventions such as parental controls rather than sweeping measures on access.

Campaigners are urging the Lords to reject the government’s approach and instead back a tougher proposal led by the Tory peer John Nash. His amendment would force the government to raise the minimum age for children accessing social media platforms to 16 within 12 months.

Peers have already backed Lord Nash’s proposal three times, most recently by a margin of 126 votes. But the government used its Commons majority to block the change, prompting its reintroduction at a critical late stage of the bill’s passage.

Since the prorogation of parliament is expected in the next week, Monday’s vote will be seen as a last opportunity for peers to force the issue back on to the political agenda. If the bill does not complete its passage in time, the government risks losing it entirely.

Nash, a former Conservative schools minister, accused the government of saying one thing and legislating for another, arguing the new amendment contradicted assurances that action would come quickly.

“It is hard to see the government’s position as anything other than deliberate deception,” Nash said. “They say they want action in months, not years. But they table amendments which propose waiting three years. What will change in three years?

“The platforms will grow more powerful. More children will be harmed, and tragically worse. This is not a serious proposal, and parliament should not treat it as one. Instead, today, parliament has a final chance to reject the government’s shamefully inadequate approach and vote for my amendment, which would put a commitment to raising the age to 16 on the face of the bill.

“As this bill reaches its final stages, let no one be in any doubt: I will not stop until we have that commitment.”

Last week the singer Cheryl Tweedy publicly backed a ban for under-16s, calling platforms “addictive” and “emotionally destroying”, while tech executives denied their platforms were addictive to children.

Campaigners have echoed Nash’s criticism. Ellen Roome, the bereaved mother of Jools Sweeney – who died during a suspected “blackout challenge” – said the issue was a test of political urgency. “It is beyond belief that the government now wants up to three years before it will act on social media,” she said. “And worse still, their ‘action’ could mean as little as parental controls.

“This amendment is an insult to every parent who has campaigned in memory of a child we have lost, so that other families do not have to go through what we have. How many more children will be harmed every day by the catastrophic effects of social media?”

She added: “How many more children will we lose while the prime minister gives himself the option of doing almost nothing? How does any of this square with the language we were given – that it would be months, not years before action?

“Tomorrow, parliament has a final chance to reject this charade and vote for Lord Nash’s amendment, which would raise the age limit for harmful social media to 16 within 12 months. Please – I implore them – just do it now.”

The government is expected to argue that much more time is needed to consider the evidence, particularly given the challenges of enforcing rules on global tech platforms.