The MPs are not breaking cover with direct criticism during the election campaign, but some are openly pushing for a more "relative" cap - which would link standard tariffs to the cheapest deals by capping the differential between the highest and lowest price an energy company can charge.
However, she insists her plan is different from the energy freeze proposed by former Labour leader Ed Miliband in 2015, which led David Cameron to accuse him of wanting to live in a "Marxist universe".
Theresa May will face a battle within her own party as well as with the energy companies if she decides to go ahead with a cap on gas and electricity prices.
Jeremy Corbyn vows to stay on as Labour leader regardless of election resultThe Tories were accused of stealing former Labour leader Ed Miliband's plans for an energy price freeze when the plan was first trailed last month.
The Liberal Democrats' Ed Davey said: "It is never a good idea to copy the economic strategy of Ed Miliband".
"The overcharging they estimated was running at about £1.4bn a year", he told the BBC Radio 4's Today programme.
The Confederation of British Industry (CBI) also cautioned against introducing a price cap, suggesting it could leave customers worse off than they are now.
"Labour is offering a real choice, a real alternative to the rigged system holding us back and to the Conservatives who are running our country down".
"The CMA's thorough two-year investigation identified low levels of consumers switching energy providers as a challenge, and put forward a range of recommendations to address this", Hardie said. "Further intervention risks undermining so numerous positive changes we are seeing in the market which are delivering benefits for consumers", he said.
"However the solution is not to distort the market as a whole but see through the market reforms, allow competition to drive innovation and benefits for customers, while ensuring that there is targeted support for those most in need".
If standard variable tariffs milk customers, the picture for consumers on pre-paid energy meters is not much rosier. With the Conservatives nearly certain to win a majority, it's highly likely the pledge will be carried out.
The proposal, which the Tories suggest could save 17 million households up to £100 per year, comes after five of Britain's "Big Six" energy providers announced a price hike on their standard tariffs, which are often the most expensive rates on offer.
Under the new plan, industry regulator Ofgem will set a maximum cap for standard variable tariffs, which are used by about two-thirds of households.
"It will be painful for some companies, especially those now taking advantage of customer disengagement, but it will offer consumers a safety net, protecting them from some of the worst practices of the industry whilst still allowing innovative suppliers to compete", he said.