"Unbelievable jobs numbers..these Chicago guys will do anything..can't debate so change numbers," Welch tweeted, referring to the site of the Obama campaign headquarters.
The drop in unemployment was announced two days after Obama's lackluster performance in his first debate with Romney.
Republican Rep. Allen West of Florida soon announced via Facebook that he agreed with Welch.
"Somehow by manipulation of data we are all of a sudden below 8 percent unemployment, a month from the presidential election," West wrote. "This is Orwellian to say the least."
The Obama administration was forced to defend Labor's statisticians and economists against accusations that came without supporting evidence.
"No serious person ... would make claims like that," said Alan Krueger, chairman of the White House Council of Economic Advisers.
The monthly jobs report is prepared with raw data collected by Census workers. The workers interview Americans in about 60,000 households or visit them door-to-door.
People are asked whether they're employed and, if so, whether their jobs are full or part time. The Census workers gather other information about the respondents' education, age and gender and ask whether they're self-employed.
Most of the interviews are done in the week that includes the 19th day of the month. The resulting pile of data is transferred securely by Census to BLS about a week before the jobs report is due.
The office suites where the report is prepared and compiled goes on lockdown. Employees can't access the area without a hard pass. Staffers working on a paper copy of the report are expected to keep it under lock and key if they aren't at their desk -- even when they go to lunch.
The security isn't just about keeping the data free of political pressure. The unemployment figures, if leaked early, could improperly move financial markets.
Tom Nardone, a 36-year veteran of the BLS, oversees the report's preparation. The goal, Nardone said, is to make the report as accurate and "apolitical" as possible.