FRESNO, Calif. (KSEE/KGPE) – The vote numbers continue to trickle in for two potentially huge races in the balance of power for the U.S. House of Representatives.

Meanwhile, races have tightened in California’s Congressional Districts 22 and 13. As of Monday, the District 22 matchup between Republican David Valadao and Democrat Rudy Salas is a difference of nearly 3,000 votes – but only 53% of votes have been counted, according to the Associated Press.

In California’s Congressional District 13, Republican John Duarte has a razor-thin lead over Democrat Adam Gray, with just an 84-vote difference – and only 61% of votes have been counted in that district.

So what is the hold-up? Officials say part of it is the process to verify mail-in ballots.

“It’s a timely process to check every signature, flatten every ballot. All of that takes time,” said Donna Linder, Registrar of Voters in Stanislaus County.

As of last Thursday, Stanislaus County had roughly 40,000 votes still to count, as mail-in ballots have continued to come in. Another part of the issue is election officials who took the long weekend off to recharge.

“The more tired your staff, the more potential for mistakes,” said Linder. “So, I make sure my staff is rested. I know people are anxious to hear the results. But I’d rather have accuracy. So.. then speed,” she said.

As of Monday, Stanislaus County does not have a projected finish date in sight.

In District 22’s Tulare County, election employees also took time to rest. There are roughly 35,000 ballots left to be counted there as of Monday. The county’s registrar of voters hopes to certify the election soon.

“We will be staying late and probably every night this week to get the election certified by next week,” said Michelle Baldwin, Tulare County’s registrar of voters.

When the races do become certified, they could be key to deciding who controls the U.S. House of Representatives.

“Congressional District 22 and Congressional District 13 are going to be a big part of determining whether Democrats or Republicans have control. So a lot of eyes are gonna be watching very carefully to see how um, you know, 22 and 13 come out,” said Tom Holyoke, political analyst and Political Science professor at Fresno State.

Officials have until December 9 to certify the elections.