"The premier needs to think carefully about the fact that he was given quite a different mandate this time around," said leader Andrea Horwath after her first meeting with her new caucus.
"You can work with a lot of hubris and a lot of puffiness in your chest but the bottom line is when it comes to actually delivering for the people you have to have some humility in that ... and not play a lot of games and not play a lot of arrogant lines."
The NDP and the Tories, with 54 seats between them, would be able to bring down the Liberal government if they chose. But Horwath said she wants to wait and see how the parties behave when the legislature resumes.
"It would be irresponsible of me to simply say: 'My way or the highway' on any issue," she said.
Horwath wouldn't impose a deadline for the Liberals to show they're willing to play by her rules, and suggested she'd be willing to work for another four years under a minority situation because voters want stability.
But she added it's important that Premier Dalton McGuinty and Progressive Conservative Leader Tim Hudak "respect that as well."
Before the caucus meeting, Horwath appointed Toronto's Cheri DiNovo as the party's chief whip and northeastern Ontario's Gilles Bisson as house leader.
She also said Thursday she had commitments from all 17 NDP members that no one will cross the floor to give the Liberals a majority, and is declining to nominate any of them for the role of Speaker because that would mean any vote could end in an even split.
"It's really clear that we have a minority government where we really can't give up any seats to the Speaker's position," said Horwath. "I talked to all of my team about that — they all agree."
The Liberals won 53 seats in the election, just one short of a majority, which means that going into the next legislative session, every vote will count.
The Progressive Conservatives and the Liberals have yet to make their appointments, and it's still unclear when the Tories or Liberals will be meeting with their newly elected members.
The Progressive Conservatives have held no media events since Hudak won 12 additional seats but lost the election in which he was the initial front-runner.
It is expected they won't nominate anyone for Speaker either, forcing the Liberals to give up one of their members for the role.
Since the Speaker cannot be a cabinet minister, McGuinty will have to name his ministers before a Speaker can be elected.
Conservatives Elizabeth Witmer and Ted Arnott have both said they wouldn't accept a nomination.