As an immigration reform bill grinds its way through Congress, Florida Senator Marco Rubio has emerged as perhaps its most crucial broker. The rising Republican star has put reform at the center of his political ambitions, using his conservative bona fides to round up GOP votes while negotiating hard to add additional enforcement measures to the legislation.

Rubio’s starring role may also provide opportunities for a company whose business could be substantially affected by the bill’s outcome: the private prison company GEO Group, which operates many of the federal facilities that hold detained or incarcerated immigrants. Rubio is the Senate’s leading career recipient of contributions from the Florida-based company, garnering $27,300 in support, according to data compiled by the Center for Responsive Politics. And there are close ties between his staff and the GEO Group’s lobbyists.

The reform debate has many threads worth watching and many interest groups that merit journalistic attention. But as formal debate opens in the Senate next week, reporters and other observers should set aside some time to keep watch on the GEO Group’s activities—and how the legislation that emerges from the Senate would affect it and other private prison companies.

On Wednesday, a report by The Nation provided new revelations about GEO Group’s links to Rubio. The company has pledged not to participate in the reform debate, but the report featured records showing that GEO Group had employed the firm Navigators Global to lobby Congress in the first quarter of 2013 on “issues related to comprehensive immigration reform.” Navigators Global was co-founded in 2003 by Rubio’s current chief of staff, Cesar Conda.

Conda plays a prominent role in Rubio’s immigration reform outreach. He left Navigators Global when he took his position with Rubio in January 2011. He has continued to receive payments from the lobby firm after his departure due to a buy-out agreement on his shares, according to an earlier report from The Investigative Fund at The Nation Institute.

In the wake of this week’s report, GEO Group said that it is not seeking to pass or defeat the reform bill, and that Navigators Global lobbied Congress on a single narrow issue.

“Our company’s discussions have been aimed at educating lawmakers exclusively and entirely on the existing Alternatives to Detention program, in which our subsidiary, BI Incorporated, is a contractor to ICE,” Pablo Paez, a spokesman for GEO Group, wrote to CJR via email. “Our company has not lobbied to influence immigration policy nor have we taken nor will we take an overall position on immigration reform legislation.”

The Alternatives to Detention program allows undocumented immigrants in removal proceedings to avoid being held in detention by participating in alternative approaches, such as case management and electronic monitoring.

The company did not respond to a question about whether it had discussed immigration reform with Rubio or his staff. A spokesman for Rubio did not respond to an email inquiry from CJR.

Of course, Rubio is not the only important lawmaker in the reform debate. Any comprehensive bill will face a harder path in the GOP-controlled House than in the Senate, and there were reports this week that talks in the House were in trouble. Enforcement concerns are among the roadblocks, and any bill that passes will have to draw at least some support from a House Republican caucus that puts a strong emphasis on border security.

But Rubio has staked out a central role for himself in setting the agenda and brokering deals on enforcement—all the more reason why his ties to GEO Group merit attention.

On Tuesday, Rubio told radio host Hugh Hewitt that he would likely vote against the immigration bill, which he initially helped craft, unless it was amended to beef up border enforcement. Among Rubio’s demands was that Congress, rather than the Department of Homeland Security, should be in charge of deciding whether the crucial “trigger” condition of a secure border had been met. This trigger would be a precondition for a path to citizenship for the undocumented.

Sasha Chavkin covers political money and influence for CJR's United States Project, our politics and policy desk. He has written for ProPublica, the Center for Public Integrity, and The New York World. Follow him on Twitter @sashachavkin.