(CNN) The Environmental Protection Agency is planning to reduce its workforce through buyouts and an early retirement program, according to an internal memo obtained by CNN. The memo also said the agency plans to continue to maintain a hiring freeze, with "very limited exceptions," even as the government-wide freeze expires.

CNN reported last week that 350 jobs went unfilled at the EPA under the Trump administration's hiring freeze , and no new positions could be created.

The internal memo said the agency hopes to complete the buyout program by the end of FY 2017.

John O'Grady, president of AFGE Council 238, the union that represents EPA employees, said: "This Administration wants to cut at least 3,100 full-time employees, yet the March 21, 2017, budget document indicates cuts as high as 4,000 full-time employees." O'Grady said buyouts and early retirements won't achieve that goal, because the math makes it unrealistic.

In 2014, "the US EPA paid incentives of about $11.3 million to get 456 employees to voluntarily leave the agency, plus accumulated annual leave payments of $4.9 million, for a total of $16.2 million," O'Grady said. "That amounts to approximately $35,526 per employee on average. For the agency to use the same procedure to try and encourage 1,000 or more employees to voluntarily leave the agency would be exorbitantly expensive, costing more than $36 million per 1,000 full-time equivalents."

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