Crossroads GPS, the most well-funded Republican-leaning outside group in politics, is jumping on board the immigration reform effort.

In a series of newspaper advertisements in Washington, the group effectively stakes out the same position that Sen. Marco Rubio (R-Fla.) has in recent days, being broadly supportive of the effort but urging the adoption of certain amendments, including more border security.

The group is urging Congress "to move forward with legislative changes to secure the border, allow for high-skilled immigration, prohibit eligibility for welfare and Obamacare benefits, put undocumented immigrants at the back of the line, and replace the current chain migration system to one that is merit-based," according to a news release.

"The Senate immigration bill needs an 'extreme makeover' before we can say it really protects our borders and our workers, but it's important that Congress move forward on it and not just throw up its hands," said Crossroads GPS CEO Steven Law.

The ads cost about $100,000. They are signed by business and political leaders including former Florida governor Jeb Bush, former senator Norm Coleman (Minn.), former Puerto Rico governor Luis Fortuno and Crossroads founder Karl Rove.

It's the first time Crossroads has signaled a position on the immigration legislation, which is headed for intense debate on the Senate floor. Opponents say the bill is de facto amnesty and that it doesn't include enough border security to prevent another influx of illegal immigrants; proponents worry that the amendment process could result in a bill that cannot be passed because it effectively cancels out the path to citizenship.

The bill gained a crucial supporter Sunday when Sen. Kelly Ayotte (R-N.H.) jumped on board. Her support suggests the bill is nearing the 60 votes it needs to overcome a filibuster in the Senate. Of course, even if it passes the Senate, its fate in the House is far from certain, given the GOP's majority in that chamber and the fact that it last week passed a bill to override President Obama's executive order exempting young illegal immigrants from deportation.

Sen. Charles Schumer (D-N.Y.), a member of the so-called Gang of Eight that drafted the bipartisan bill, has said he expects to pass it out of the Senate by July 4.