PEMBROKE PARK, Fla. – A lawyer for U.S. Sen. Bill Nelson's re-election campaign is suing Florida Secretary of State Ken Detzner, claiming that the state is disenfranchising voters by not accepting mail-in ballots received after Election Day.

Marc Elias, an attorney representing Nelson and the Democratic National Committee, filed the lawsuit Monday morning in federal court.

"No Floridian should have their rightful vote denied because of mail/post office delays," Elias said on Twitter. "We are suing to protect these ballots."

BREAKING: No Floridian should have their rightful vote denied because of mail/post office delays. We are suing to protect these ballots. #CountAllTheVotes — Marc E. Elias (@marceelias) November 12, 2018

According to the lawsuit, nearly 3.5 million Florida voters requested to vote by mail, but as of Thursday -- two days after the general election -- "a staggering 874,818 of those VBM ballots has not yet been counted as returned."

File: Democrats vs Florida Secretary of State

Under Florida law, mail-in ballots are only counted if received by the supervisor of elections by the 7 p.m. deadline on Election Day.

"Conditioning the validity of ballots solely on a 'received by' date, rather than coupling the 'received by' date and a postmark date -- which is the case for overseas voters -- all but ensures that qualified voters submitting VBM ballots can be denied the right to vote based entirely on arbitrary factors beyond their control, like mail delivery speed," the lawsuit said.

It cites the Oct. 25 incident at the U.S. Postal Service's mail distribution center in Opa-locka as an example. That was when several pipe-bomb packages addressed to prominent Democrats were discovered to have been processed through the facility, leading to a bomb scare.

Suzy Trutie, a spokeswoman for the Miami-Dade County Elections Department, told CNN there were 266 ballots in a shipment that came from the Opa-locka facility that won't be counted because they did not meet the standard.

"Voters should not be disenfranchised solely due to the speed of the post office's delivery," the lawsuit said.

The lawsuit seeks to count all ballots postmarked before Nov. 6 and received by the supervisor of elections within 10 days after Election Day.