In a thinly veiled threat to congressional Republicans, President Obama Tuesday warned the GOP not to obstruct a comprehensive immigration-reform bill being debated in the Senate this week.

“If you’re actually serious and sincere about fixing a broken system, this is the vehicle to do it — and now is the time to get it done,” Obama said from the East Room of the White House. “There is no good reason to play procedural games or engage in obstruction just to block the best chance we’ve had in years to address this problem.”

Obama called for lawmakers to coalesce around an immigration fix by the end of the summer. Earlier in the day, House Speaker John Boehner, R-Ohio, talked about reaching a solution by the end of the year.

Politicians, so-called DREAMers, business leaders, law enforcement officials and labor figures joined the president on stage, people Obama said shared few political beliefs but are united on the issue of immigration.

For the most part, Obama has steered clear of immigration negotiations, hoping not to alienate conservatives who might support a pathway to citizenship for the nation’s 11 million illegal immigrants. But Obama changed tactics on Tuesday, dismissing GOP charges that the bill produced by the so-called Gang of Eight amounted to amnesty for lawbreakers.

“Yes, they broke the rules, they didn’t wait their turn,” Obama said of those living in the U.S. illegally. “They shouldn’t be allowed off easy; they shouldn’t be allowed to game the system.”

In essence, Obama was hoping to paint those against the Gang of Eight blueprint as outside the mainstream, saying a majority of Americans support the reforms.

And the president talked tough about border security amid Republican complaints that the immigration-reform package has no clear system for measuring whether the border is secure, saying such reforms were “no cakewalk” for those looking to obtain citizenship.

“Illegal crossings are near their lowest level in decades,” Obama said. “Nobody is taking border enforcement lightly.”

It remains to be seen how Obama’s heightened rhetoric after months of virtual silence will shape the immigration debate. Some liberals had asked him to stay out of the way so Republicans could avoid charges that they were rubber-stamping Obama’s second-term agenda.