Theresa May compared Jeremy Corbyn with an "unscrupulous boss" as she made her Prime Minister's Questions debut.
As the two leaders clashed on workers' rights, Mrs May suggested Labour frontbenchers had to "double their workload" while Mr Corbyn "exploits the rules to further his own career".
Mr Corbyn said Tories might find economic insecurity "funny" but millions of people did not.
The Labour leader said the government's economic plan had "failed".
"Is there another one?" he asked.
Mr Corbyn said austerity meant people "being poorer" and "jobs being cut", prompting Mrs May to respond: "He calls it austerity. I call it living within our means."
- Live coverage of PMQs including reaction
The Labour leader also raised the decline in home-ownership among young people and criticised the £450,000 upper limit - which applies in London - for prices under the government's flagship starter homes scheme.
Mrs May said this was because house prices varied across the country.
In a reference to Labour's leadership election, she said the Opposition would spend the summer "tearing itself apart" while the government would be "bringing this country back together".
After PMQs, Mrs May will travel to Berlin to meet her German counterpart Angela Merkel.