MPs have written to new business secretary Greg Clark, urging him not to implement a Competition and Markets Authority recommendation which would no longer require energy price comparison sites to show potential switchers the whole market.
The energy and climate change committee warned that the move could undermine consumer trust in the energy market and strangle competition.
It also urged the government to ensure a new database of customers who have been on their energy supplier's default tariff for three years of longer doesn't lead to privacy breaches or nuisance marketing.
It comes after the competition regulator delivered a widely-criticised set of recommendations last month, following its two-year investigation into whether the big six energy suppliers had been overcharging customers.
Angus Brendan MacNeil, chair of the energy and climate change committee, wrote: "Ofgem referred the energy market to the CMA for an investigation in order to 'clear the air' after public trust in the energy market had collapsed in 2013-14."
"That trust is gradually returning, as Ofgem's latest survey of public attitudes to the energy market shows. This remedy risks turning that tide and eroding trust afresh.
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"We are [also] concerned that this remedy would have a detrimental effect on competition … it would be counter-productive and ironic, if the CMA investigation led to a remedy that inadvertently reinforced the dominance of the big six and made it harder for new entrants to reach potential customers."
Luke Watson, managing director of GB Energy, added: "We urge the government to work with us and other small energy suppliers to find an alternative solution which ensures that bill payers get the best possible deals."