WASHINGTON – As the U.S. Border Patrol’s Buffalo sector has stepped up its efforts to arrest illegal immigrants, it may also have vastly expanded a bonus system that can reward agents with cash, extra vacation time and even Home Depot gift cards.

And perhaps as a result, 277 of those arrested on immigration charges between 2006 and 2011 by agents based in Rochester – who are part of the Buffalo sector – were in the U.S. legally and should not have been arrested.

Those were the key conclusions of a report by Families for Freedom, a New York based immigrant advocacy group, and the New York University Immigrant Rights Clinic – a report that prompted Sen. Kirsten E. Gillibrand to voice serious concerns in a letter to Homeland Security Secretary Janet Napolitano.

A focus on arrest rates, “coupled with a policy of rewarding arresting agents with bonuses, casts doubt over the fairness of each arrest,” Gillibrand, D-N.Y., said in the letter, which her office released Wednesday.

“Indeed, agents may be more likely to employ discriminatory methods such as racial profiling simply to bolster their arrest totals,” Gillibrand said.

Families for Freedom said it uncovered the focus on arrests and the bonus program through a Freedom of Information Act lawsuit, which produced records detailing the Border Patrol’s work in the 29 New York and Pennsylvania counties in the Buffalo sector.

The resulting information probably reveals just a snippet of what’s likely a national program to reward Border Patrol agents for the number of arrests they make, claimed Abraham Paulos, executive director of Families for Freedom.

“The report is really about what we don’t know,” Paulos said. “This is just a window into the Border Patrol’s culture of policing.”

In a statement, though, the Department of Homeland Security denied rewarding Border Patrol agents for their arrests.

“No such practice of paid incentives and awards for specific human targets or enforcement actions has ever occurred within the Border Patrol, nor will it ever occur within the ranks of any [Customs and Border Protection] component,” the statement said.

Asked what the bonuses were paid for, then, agency spokesperson Joanne Ferreira would only say: “Got to refer you to the statement.”

And while the Border Patrol had earlier denied that it keeps track of arrests by agents in its various stations, the Families for Freedom lawsuit revealed that the agency keeps meticulous records on how many arrests are made each day, and where they occur.

“USBP’s policy of closely monitoring and circulating arrest numbers encourages stations and individual agents to focus their efforts on making as many arrests as possible,” the report said.

Meanwhile, Families for Freedom’s efforts also revealed that the Border Patrol has three separate incentive programs for agents in its Buffalo sector.

Agents can get cash awards of up to $2,500 a year, time-off rewards of up to 40 hours and $100 gift cards from Home Depot and other retailers.

“The documents produced in the litigation show that this program allows station managers to recommend cash bonuses to arresting agents on a discretionary basis,” Families for Freedom said, adding that it only made sense that for agents, more arrests would result in a bigger bonus.

Families for Freedom said the cash award bonus program has been in place for several years, and that the money spent on it annually had grown from $6,000 in 2003 to $194,890 in fiscal 2011.

What’s more, as the bonus program has grown, so has the Border Patrol’s propensity for arresting the wrong guy.

Families for Freedom’s lawsuit produced arrest records in the Border Patrol’s Rochester station, which is part of the Buffalo sector. According to those Rochester records, 277 people were arrested improperly between 2006 and 2011.

“The actual number is probably far higher because CBP did not formally instruct its agents to document these arrests until June 2010,” the Families for Freedom report said.

Twelve of the people arrested improperly were U.S. citizens and 52 were permanent legal residents, while the rest either had valid visas, were involved in pending immigration proceedings or had been granted asylum in the U.S.

Africans, Asians and Middle Easterners made up the vast majority of those arrested improperly, the records show, prompting Gillibrand to question whether racial profiling was taking place.

“I implore the department to implement data-collection mechanisms to detect any pattern of potentially discriminatory conduct,” Gillibrand said in her letter.

In addition, Gillibrand’s office said the senator plans to introduce legislation that will force federal agents and local law enforcement officers working with them to record why people are being stopped, their demographic characteristics, their immigration status and other key information.

That information would have to be compiled and reported to Congress annually.

In the meantime, though, Gillibrand sought immediate action on the issue from Napolitano.