The Conservative leader, who is battling to assert her authority after last month's disastrous general election, drew loud cheers from her MPs when she insisted that Britain must "live within our means".
In a robust exchange in the House of Commons, opposition Labour leader Jeremy Corbyn accused the government of "flip- flopping and floundering" over whether to raise wages for teachers, nurses and other public-sector workers.
Foreign Secretary Boris Johnson, Defence Secretary Michael Fallon and Environment Secretary Michael Gove have all indicated they would support lifting the pay freeze on around five million people.
The confusion led to accusations that May was no longer in control of her government, after losing her party's majority in parliament in the June 8 vote.
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During her weekly question time, May said she would consider "very carefully" recommendations from pay review bodies.
But she warned: "We need to balance the need to be fair to public-sector workers, to protect jobs in the public sector, and to be fair to those who pay for it."
"When Tories talk of tough choices, we know who suffers -- it's the poorest and most vulnerable in our society," he said.
May countered that she valued public-sector workers, adding: "The difference is, I know we have to pay for them."
May warned that Labour's plans to increase public spending could see Britain go the way of debt-laden Greece -- an accusation a senior party source later said was "preposterous".