Australia is introducing a world-first law to make Google, Facebook and potentially other tech companies pay media outlets for their news content.
But the US firms have fought back, warning the law would make them withdraw some of their services.
Australian PM Scott Morrison said lawmakers would not yield to "threats".
Australia is far from Google's largest market, but the proposed news code is seen as a possible global test case for how governments could seek to regulate big tech firms.
Tech firms have faced increasing pressure to pay for news content in other countries, including France, where Google struck a landmark deal with media outlets on Thursday.
In Australia, the proposed news code would tie Google and Facebook to mediated negotiations with publishers over the value of news content, if no agreement could be reached first.
Google Australia managing director Mel Silva told a Senate hearing on Friday that the laws were "unworkable".
"If this version of the code were to become law, it would give us no real choice but to stop making Google Search available in Australia," she said.
But lawmakers challenged this, accusing Google of "blackmail" and bullying Australia for raising the reform.
Mr Morrison said his government remained committed to progressing the laws through parliament this year.
"Let me be clear: Australia makes our rules for things you can do in Australia. That's done in our parliament," he told reporters on Friday.