RICHMOND, Va. (WRIC) — The U.S. Postal Service sent a letter to the commissioner of Virginia’s Department of Elections, along with the majority of the country’s election officials, warning that not all mail-in ballots for the November election are guaranteed to arrive in time.

In the letter, which 8News obtained, the Postal Service’s general counsel and executive vice president, Thomas J. Marshall, lays out the issues that could prevent ballots submitted near the deadline from being counted.

“The purpose of this letter is to focus specifically on the deadlines for requesting and casting ballots. In particular, we wanted to note that, under our reading of Virginia’s election laws, certain deadlines for requesting and casting mail-in ballots may be incongruous with the Postal Service’s delivery standards,” Marshall writes to Virginia Elections Commissioner Christopher Piper. “This mismatch creates a risk that ballots requested near the deadline under state law will not be returned by mail in time to be counted under your laws as we understand them.”

Gov. Ralph Northam (D) called the Postal Service’s warning “a deeply troubling development” on Friday.

“This is a deeply troubling development in what is becoming a clear pattern of attempted voter suppression by the Trump administration,” Gov. Northam said. “I am committed to making sure all Virginians have access to the ballot box, and will continue to work with state and federal lawmakers to ensure safe, secure, and accessible elections this fall.”

On Sept. 18, Virginia residents eligible to vote can do so early by going to their local registrar’s office. The period for in-person absentee voting starts that day and ends on Oct. 31.

This story is developing. Check back for updates.