Postal workers on Friday plan to protest nationwide against proposed plant closings and declining service standards that have led to slower mail delivery throughout the country.

The American Postal Workers Union said it will hold demonstrations at the U.S. Postal Service’s last Board of Governors meeting of the year in Washington and at 100 other locations, including locally in Baltimore, Norfolk, Richmond and Roanoke.

“The cuts would cause hardships for the public and small businesses, eliminate jobs and destroy the world’s most efficient and affordable delivery network by driving away mail and revenue,” the labor group said in an announcement.

The Postal Service is scheduled to close 82 mail processing and distribution centers nationwide in January as part of a plan to cut costs by $20 billion over the next few years. The agency has already shuttered 300 of the facilities since 2006.

The next round of closures is expected to save $750 annually, according to USPS estimates.

The Postal Service also reduced its service standards in 2012 in an effort to save money, increasing the number of days it takes to haul the mail to a given destination.

As an example of the changes, the USPS now aims to deliver mail within three days when an item needs to travel a distance of 12 driving hours, whereas the agency previously tried to deliver mail that distance within two days.

A recent Government Accountability Office report said first-class mail performance has generally declined this year because of the relaxed standards, with the Postal Service missing its target delivery times at a greater rate than before. But the changes have not affected periodicals and packages, according to the USPS.

The Postal Service downplayed the findings in the GAO report, saying they do not represent performance across all districts and adding that severe weather may have contributed to longer delivery times during the first half of this year.

Agency spokesman Toni DeLancey said all of the recent changes are good for the organization and its long-term viability.

“Our mail-processing machines are sitting idly for many hours of the day, and we are losing billions of dollars every year,” DeLancey said. “It would be irresponsible for us not to make the changes needed to adapt to this environment. We owe it to the American economy. We owe it to our customers. And we owe it to our employees.”

The USPS has experienced massive financial losses for the past several years, shedding billions of dollars annually in large part because of declining mail volume and a 2006 congressional mandate that requires the agency to prefund its retiree health benefits at a cost of more than $5 billion a year.

The USPS reported a $2 billion loss during the third quarter of this year alone, and the agency is expected to reveal more red ink when it releases its fourth-quarter financials later this month. USPS officials have already said the organization will have to default on its prefunding requirement for the fourth consecutive year.

Postal unions have been highly critical of the congressional mandate, arguing that the USPS could earn a profit without it. Postmaster General Patrick Donahoe has asked lawmakers to remove or revise the requirement, but agency officials say the organization would still lose money in that case because of debt.

The American Postal Workers Union said service-standard reductions and plant closings are unnecessary, noting that USPS finances have improved for four years in a row. With the agency earning a $1 billion operating profit so far this year, union officials say the organization could stop losing money if not for the prefunding mandate.

“There is red ink, but it stems from political interference, not from the mail,” the American Postal Workers Union said in its protest announcement.

More than half of the Senate and 160 House members have called for a one-year moratorium on the service reductions and plant closings.

An agreement on postal-reform legislation has eluded lawmakers for several years, with opposition coming from both parties because the plans would involve service cuts such as an end to Saturday mail delivery. It is unclear whether the recent midterm elections, which gave Republicans a majority in both chambers of Congress, will change matters.