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A third of the U.S. Secret Service agents working long hours to protect Donald Trump and Hillary Clinton aren't being paid for overtime, despite their grueling schedules in an unusually hectic election year.

"When you're expecting people to be away from home for weeks at a clip, working 16-hour days, there should be some reward for it," said Patrick O'Carroll, executive director of the Federal Law Enforcement Officers Association.

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Unlike many federal employees, Secret Service agents do qualify for overtime pay. But because of a government-wide limit that caps their salaries at $160,300, more than 1,000 agents have maxed out and haven't been paid for working overtime since the spring.

Agents are caught in a squeeze. A hiring freeze has limited their numbers, while 2016 has put unusual demands on the Secret Service, with two political conventions, a meeting of the UN General Assembly, a nuclear summit, and candidates with ambitious travel schedules confronted with often boisterous crowds.

The pace this year, say agency veterans, has been brutal. Agents have worked to secure events at 7,700 locations and have screened more than eight million people.

The elite protective division is now responsible for the security of 26 VIP’s — including President Obama and Vice-President Biden and their families, the presidential and vice-presidential candidates and family members, four former presidents, and some other top federal officials.

Some members of Congress are working on a fix that would lift the overtime cap, an effort which the Secret Service supports. One measure would apply only in presidential election years.

"The silent professionals of the Secret Service and their families make tremendous sacrifices every day to ensure those we protect are safe. The demands placed on Secret Service employees during a campaign year are especially daunting," says a statement from the agency.

Rep. Elijah Cummings, a Maryland Democrat, saod he's optimistic Congress can act this year to let agents be paid the overtime they've earned.

"Many of them have told me they'll take a bullet for the president. We ought to be able to properly compensate them," said Cummings.