The $1.3 trillion spending bill that President Donald Trump signed last month contained a subtle yet dramatic shift for U.S. senators.The budget for "Senate operations," the pocket of money members use for staffing, grew from roughly $871 million last year to $920 million for 2018 - a bigger raise (6 percent) than from 2014 to 2017 (1.4 percent).Carlos Mark Vera, founder of advocacy group Pay Our Interns, saw the extra cash as an opportunity to pressure U.S. leaders into changing a norm he says is troubling.Read More: Florida Democrats challenging more legislative seats this yearMost congressional interns aren’t paid at all. So, he said, college students who nab the positions rely on funds from parents or work part-time jobs on top of their hectic Washington schedules."I was fighting not to fall asleep," Vera said of interning for former Rep. Joe Baca, D-Calif., without pay in 2012 and simultaneously working as a front-desk assistant at American University.Plus, he said, he was one of the only Latinos around. Four-fifths of voting members in the House and Senate are white, according to the latest numbers from the Pew Research Center."Something I vividly remember," he said, "was walking down the hallways of Congress and realizing no one looked like me but the janitors."On Thursday, Vera started sending letters to senators of both parties who do not offer paid internships, urging them to consider the rising cost of living in Washington, where the median monthly rent for a one-bedroom apartment is about $2,000."I write to encourage your office to take action and use some of the surplus funds to launch a paid internship program," he wrote, "so that, once again, opportunities on Capitol Hill are open to all young people, and not just those who can afford to work for free."The Senate’s budget increase breaks out to about $100,000 in extra cash per office, Vera said. The House got a more modest boost ($11 million) for operations in the latest spending bill.A study last year by Pay Our Interns found that 51 percent of Republican senators offer paid internships, compared with 31 percent of Democrats.House interns fare worse: Only 8 percent of those who work for Republicans and 3.6 percent who work for Democrats get paid.Representatives from neither party responded to The Post’s request for comment.Even political leaders who push for a higher minimum wage expect students to work for them for free, advertising the internships as valuable learning experiences that could open the door to a prestigious Capitol Hill job.Among those who offer unpaid internships: Senate Minority Leader Charles E. Schumer, D-N.Y., Sen. Tammy Duckworth, D-Ill., and Sen. Amy Klobuchar, D-Minn., who have all promoted the "Fight for $15" minimum wage campaign.Audrey Henson, founder of College to Congress , a group that helps students pay for rent and work clothing in Washington, said she took out loans to intern for Sen. Marco Rubio, R-Fla., and Rep. Eric A. "Rick" Crawford, R-Ark.Her first summer, Henson said, cost her $6,500."I came from a single-parent household," she said. "This system is not designed for people like me to break into it."Brad Fitch, chief executive of the Congressional Management Foundation, which has designed training manuals for Capitol Hill interns, said the operations budget is typically tight for lawmakers. Junior staffers tend to make about 20 percent less money than their counterparts in the private sector."Do you pay interns or do you give younger staffers the bonus?" he said of a congressional manager’s dilemma.The funding increase on the Senate side, though, could give leaders more flexibility with labor decisions."This is the first genuine increase in their budgets in decades," Fitch said.