"Members, we ask for more time given the fact that the U.S. Supreme Court is to hear Trump v. Boockvar in the coming days," the letter to Senate Majority Leader Mitch McConnell and House Minority Leader Kevin McCarthy reads.
In the letter, the Pennsylvania senators accuse State Secretary Kathy Boockvar of "allowing for a proliferation of unsecured drop boxes in key Democratic areas" and "encouraging some counties" on the day before Nov. 3 to "notify party and candidate representatives of mail-in voters whose ballots contained disqualifying defects and allowing them to 'cure' those defects."
Among the signers were President Pro Tempore Jake Corman, Republican Majority Leader Kim Ward, and state Sens. Judy Ward and Kristin Phillips-Hill.
Lawmakers also argue in the letter that mail-in ballots were counted three days after officials received them, ballots without postmarks were counted and signatures on ballots were not verified, as state law requires.
The letter concludes by asking McConnell and McCarthy, who on Sunday expressed support for a Republican-led challenge to the Electoral College's election certification in a statement to The Hill, to "delay certification" as the State Senate pursues "election integrity" in the Commonwealth.
Congress will hold a joint session Wednesday at 1 p.m. ET to certify the presidential election results.
More than a dozen Senate Republicans have said they will object to the certification of results in at least one state, and more than 100 House Republican members said they plan to object to results in Arizona, Michigan, Wisconsin, Pennsylvania, Nevada, and Georgia.
But other Republicans, including McConnell, R-Ky., Sens. John Thune of South Dakota, John Cornyn of Texas, Mitt Romney of Utah, Susan Collins of Maine, Lisa Murkowski of Alaska and Tim Scott of South Carolina, among others, have committed to voting to certify the election results.
Fox News' Brooke Singman contributed to this report.