As a condition of a guilty plea, a Copiague construction company has agreed to back pay more than $100,000 for nine employees and also will pay a $5,000 fine, Nassau County prosecutors said Thursday.

Tri-Rail Construction Inc. also agreed to reimburse Nassau County $15,000 for the cost of investigating charges that Tri-Rail paid the employees only a fraction the hours they worked in a nine-month span, according to a news release from the office of District Attorney Kathleen Rice.

Rice said her office's Labor Unit found that from October 2010 to July 2011 Tri-Rail shorted the employees pay for work on an environmental improvement public works project at Stannards Brook Park in Port Washington.

The investigation, which began in July 2011, also found the company falsified payroll records submitted to Nassau County, the release said.

Employees worked on drainage system between streets, the park, and Manhasset Bay, renovated all walkways and bridges in the park, and replaced and repaired the park's retaining walls, the release said.

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The workers were shorted $100,895, including one worker who was owed $30,500, Rice's office said.

Rice said in a prepared statement that the "employees performed excellent work" and called the employer's actions "shameful."

Since Rice founded the Labor Unit in 2006 it has a 100 percent conviction rate, the release said.

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Workers who think they may have been victimized can call the Labor Unit at 516-571-1300.