Fears that dozens of companies providing these pensions are too small to survive were explored in a recent BBC investigation.
Now Pensions Minister Ros Altmann has told MPs that legislation is needed to "ensure proper protection" for savers.
She said that she was pushing for a slot for a law to be proposed.
"We know that doing nothing is not an option," she told the Work and Pensions Select Committee.
Workers are being automatically enrolled into a workplace pension by employers in a rolling programme set out by the government, although employees are free to opt out.
So-called Master Trust schemes, which manage pensions, are popular with the 1.8 million small employers with fewer than 30 staff who are currently signing up staff under the auto-enrolment programme.
Only five have some kind of kitemark, and The Pensions Regulator told the BBC that there was a risk that some of the smaller schemes might not survive, putting savers' money at risk.
This was confirmed by Baroness Altmann, who said that there were concerns over some of the smaller operators among the 72 Master Trusts in the UK.
She said that savers' pensions could be affected if these trusts went under, because the wind-up costs faced by the trusts could effectively eat into these savings.
Protection required a new law, she said, adding that she was "pressing for a pensions bill" to do so. This has yet to be put into the government's legislative programme.
MPs on the committee asked why this protection was not in place when the auto-enrolment system was set up.
Charlotte Clark, director of private pensions at the Department for Work and Pensions (DWP), admitted that the number of trusts that had been set up had taken the DWP by surprise.
A new law is needed to protect workers' savings held by companies that provide auto-enrolment pension schemes, a minister has said.