Boston (CNN)President Barack Obama lambasted Republican presidential candidates Monday, charging the GOP is treating American workers like a hostile force while looking out only for the rich.

Obama delivered a Labor Day speech in Boston, where he traveled to unveil a new executive order he signed forcing companies who contract with the federal government to provide paid sick leave to their employees.

Obama, saying he was relieved to not be on the ballot next November, hit at Republicans who he claimed were espousing policies that would erode the middle class.

\"We're starting to hear a lot about middle-class values,\" he said. \"Some folks seem confused about what exactly that means.\"

Without mentioning him by name, Obama struck at Wisconsin Gov. Scott Walker for answering a question about his ISIS strategy earlier this year by saying: \"If I can take on 100,000 (union) protesters, I can do the same across the globe.\"

\"He is bragging about how he destroyed collective bargaining rights in his state,\" Obama said to boos Monday. \"And [he] says that busting unions prepares him to fight ISIL. I didn't make that up. That's what he said.\"

Obama added incredulously, \"Really?\"

The president told the crowd of nearly 800 union members that organized labor had help secure basic American worker rights like weekends off and a 40-hour workweek.

And he joked if a membership is good enough for Boston's highest-profile member of organized labor, it's good enough for other working Americans.

\"Even Brady's happy he's got a union,\" Obama said, referencing New England Patriots quarterback Tom Brady, who was aided by the NFL players union in successfully fighting a four-game suspension for allegedly under-inflating footballs last year.

\"You know if Brady needs a union, we definitely need unions.\"

Obama's Labor Day announcement on paid sick leave came after a set of similar orders requiring federal contractors to boost paychecks and conditions for their workers, including expanding overtime compensation, banning discrimination based on sexual orientation and raising workers' minimum wage.

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Obama has pushed Congress to extend those new rules across the entire private sector, but met resistance from Republicans in Congress.

The proposed rule change Obama announced Monday in Boston would require firms receiving government contracts to provide an hour of paid sick leave for every thirty hours an employee works, up to seven paid sick days per year.

The order would affect 300,000 American workers who currently aren't eligible for any paid sick leave, the White House said, adding an unknown additional number of workers would be granted additional sick time.

\"Let's face it, nobody wants a waiter who feels like they have to come to work when they're coughing or contagious,\" he said. \"That's not good for anybody.\"

Opponents claim Obama has overstepped his legal authority, and groups like the U.S. Chamber of Commerce have threatened lawsuits over the President's use of executive actions to set contracting rules.

Administration officials Sunday characterized expanding access to paid sick leave as bringing American working norms into line with those of other developed nations.

\"The United States is the only country where the issue of a federal paid leave law has become a partisan issue,\" said Labor Secretary Thomas Perez, labeling current rules stuck in the \"Leave it to Beaver era.\"

\"Regrettably here, it's become a partisan issue. Certain Republicans have said we can't afford to do this,\" he said. \"This is really remarkable when you view this issue of paid leave through the global lens. The Republican Party is really out of step with conservative governments around the world.\"