Dominic Perrottet said the opposition joined protests on Tuesday and were "sharing the videos on Facebook and Tiktok."
Labor was paying lip service to the nurses and had not offered the union any concrete support, according to the Premier.
"You would expect ... that if you joined a protest that you would actually support the demands of what the protest was," Mr Perrottet said.
Labor leader Chris Minns said on Wednesday he would not commit to introducing nurse-to-patient ratios, saying it was too early to introduce policies ahead of the 2023 state election.
"I understand the Premier is cranky about Willoughby, but that's all on you," Labor's Michael Daley said during a point of order.
The comments from Mr Daley come after the seat was pushed back into doubt on Tuesday night – as only about 10 per cent of postal votes favoured Liberal candidate Tim James.
The blue-ribbon seat of Willoughby in the heart of Sydney's north shore was held for 18 years by the hugely popular Gladys Berejiklian.
The former premier built a hefty margin of 21 per cent but the Liberal Party is facing a swing against it of more than 19 per cent.
He now leads with 51.9 per cent of first party preferences, with Independent candidate Larissa Penn closing the gap to less than four points.
Veteran ABC election analyst Antony Green says local issues affected Mr James' run, including being from the right of the Liberal Party, while Ms Berejiklian was a moderate.
Voters could also have baulked that the party pre-selected a man to replace a woman.
"That's built up to produce this big swing against the Liberal Party in this seat," Mr Green said on Wednesday.
He believes the Liberals will ultimately retain Willoughby, but the swing could have federal implications for the seat of North Sydney where independent Kylea Tink is challenging Liberal backbencher Trent Zimmerman - who is yet to be endorsed.
Mr Green described Ms Penn's run as a "short campaign" with little financial backing in a "conservative" and safe Liberal seat.
"If a little known independent with not much resources can run the Liberal party a close race, how will other Independents go?
"That's the lesson from these, we wouldn't expect that Willoughby would be the doubtful seat of these four but that's what it looks like."
Treasurer Matt Kean says he's confident postal votes will favour the Liberal Party as counting continues.
"I'm confident we will get over the line but we're not going to count our chickens yet," he told Sydney radio 2GB on Wednesday.
"We will go through the process and see what the people of Willoughby decide."
"When Gladys (Berejiklian) ran in 2003 she only won by 144 votes," he said.
On Saturday, NSW voters went to the polls in four by-elections in Strathfield, Monaro, Bega and Willoughby.
Labor candidate Michael Holland looks likely to have secured Bega for the party for the first time while the ALP retained Strathfield and the Nationals held Monaro.
The final results may not be known until March 11 due to a surge in postal votes, which the NSW Electoral Commission will begin processing on Wednesday.
