A coalition of labor unions and civil rights groups have announced their opposition to a pair of nominees to the Postal Service's governing board.

The groups are opposing the renominations of Republicans Mickey D. Barnett and James C. Miller on the grounds they haven't shown a commitment to ensuring that the federally chartered mail delivery service continues to exist long-term.

"It is especially important that the board of governors be composed of individuals who have demonstrated a strong commitment to the public service role of this great institution, and who have shown an openness to exploring all reasonable, public service-oriented options which might contribute to the vitality and sustainability of the USPS. Unfortunately, on this basis, we must urge you to reject the current slate of nominees," the group said in a letter to Senate leadership.

Signers of the letter includes the Leadership Council on Civil Rights, the NAACP, the National Urban League, the National Council of La Raza, the AFL-CIO, the American Postal Workers' Union, the Service Employees International Union, and the American Federation of State, County, and Municipal Employees.

The groups object to Barnett, who was renominated by President Obama for a third term, on the grounds that he formerly lobbied for the payday loan industry. Civil rights groups accuse the private industry of preying on low-income individuals and minorities. Unions and civil rights groups have proposed the Postal Service provide an alternative to payday loans as part of an effort to crowd out the private industry. The letter expresses concerns that Barnett might use his position to pervert this goal.

"We would be deeply troubled if anyone confirmed to a leadership position within the USPS used that position to promote the sorts of practices we have seen in the payday lending industry, or to block the advancement of alternatives," the signers said.

The groups oppose Mr. Miller, a former staffer for former Sen. Pete Domenici, R-N.M., nominated by Obama to a second term, on the grounds that he has spoken out in favor of privatizing the Postal Service in the past. Labor unions have aggressively opposed privatization, which would lessen their influence over the entity. In the letter they argue that privatization would be a bad economic move.

"While proponents of privatization point to cost savings and efficiency, recent examples such as the privatization of parking meters in Chicago cast serious doubt on these assertions," they write.

Created by the federal government, the Postal Service remains under its authority, but operates as an independent business. It does not receive federal funding and must rely on the sale of postage and related products for its operation.

It has suffered economically in recent years, having reported a loss of $5.5 billion in fiscal 2014. Declines in mail volume due to the growth in online communications has been the leading factor. Labor unions have clashed repeatedly with management at the service over budget issues.