EXCLUSIVE: Lawmakers are ramping up the pressure on the Department of State to resolve a major backlog in processing passport applications that has left many U.S. travelers in limbo and in some cases forced Americans to cancel their long-planned vacations abroad. 

The latest salvo came Wednesday from House Oversight Committee Republicans who sent a letter to Secretary of State Antony Blinken asking for a briefing by Aug. 4 to explain the logjam and provide details on State Department staffing. 

The State Department told Fox News Wednesday that about 1.5 to 2 million passports applications are pending. The current wait time for a new or renewal passport is 12-18 weeks, but applicants can pay an additional $60 to rush the process. The wait time for the expedited applications is six to 12 weeks. 

PASSPORT BACKLOG SURGES TO NEARLY 2.2M AS APPLICANTS WAIT UP TO 24 WEEKS

Despite efforts by the State Department to bring more passport staff back to the office following coronavirus restrictions, the lawmakers aren't convinced there's a plan to address the serious backlog and are demanding answers. 

"It was reported last June that about half of the State Department’s passport workers had returned to their offices," Rep. Michael Cloud, R-Texas, and other GOP lawmakers wrote in a letter obtained first by Fox News. 

"More than a year later the State Department has been unable to catch up with the demand and it appears the backlog is continuing to grow. Many Americans are being forced to cancel travel plans to see family and friends because despite trying to plan ahead, they are unable to renew or obtain a passport."

The House members aren't alone in calling the delays unacceptable. 

Sen. James Lankford, R-Okla., wrote to Blinken last week about security "operational issues" that are adding several more weeks to wait times. 

And Senate Majority Leader Chuck Schumer, D-N.Y., had a news conference on July 18 flanked by frustrated New Yorkers caught in passport limbo. Schumer called attention to a couple at risk of losing their honeymoon trip and a nurse who worked the coronavirus pandemic who is poised to miss her first vacation in a year because of passport problems. 

BLINKEN: AMERICANS CAN PICK THEIR PASSPORT GENDER

The backlogs follow major passport staffing shortages due to the pandemic. In March 2020, the State Department dramatically reduced its passport operations to protect staff from the spreading pandemic. Staff is now returning, but until they are fully ramped up, Americans should expect longer processing times, according to the State Department. 

"To address these long wait times, we are surging staff at our passport agencies and centers across the country," a State Department official told Fox News on Wednesday. "We expect to be back to 97% of our workforce by mid-August. We anticipate this will allow us to process an additional 100,000 applications per month."

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Summer is typically peak passport application season, but the State Department is seeing additional volume due to pent-up demand for vacations now that COVID restrictions have eased, it said. 

"Until we are able to ramp back up, the wait time will remain 12-18 weeks for a new passport or a renewal," the official added.

Fox News' Rich Edson contributed to this report.