WASHINGTON, Nov 19 (Reuters) - The Republican leader of a U.S. House of Representatives investigative committee asked the Census Bureau on Tuesday for more information related to a media report that the monthly unemployment rate was manipulated ahead of the 2012 presidential election.

The New York Post reported that data used in the closely watched survey was faked in the final stretch of President Barack Obama's re-election campaign, when the monthly unemployment rate fell by 0.3 percentage points to 7.8 percent from 8.1 percent.

The Census Bureau rejected the allegations and said it had reported the claims to the Office of the Inspector General as soon as it learned of them.

"These allegations are shocking," Republican Representative Darrell Issa of California, the chairman of the House Oversight Committee, said in a letter to Census Bureau Director John Thompson.

The letter was also signed by Representatives Blake Farenthold, chairman of an Oversight subcommittee, and Kevin Brady, chairman of the Joint Economic Committee.

The Republicans sought a broad range of documents and communication related to the collection of data for the Current Population Survey, which is used by the Bureau of Labor Statistics to calculate the unemployment rate.

"We need to better understand whether the Current Population Survey and other important Census Bureau data are reliable, and if not, whether Census Bureau officials knowingly and intentionally fabricated the data on which they are based," the letter said.

Farenthold said in a statement that "we intend to thoroughly investigate these disturbing allegations."

Stacy Gimbel Vidal, a spokeswoman for the Census Bureau, said: "We have no reason to believe that there was a systematic manipulation of the data described in media reports."

"As a statistical agency, the Census Bureau is very conscientious about our responsibility to produce accurate Current Population Survey data for the Bureau of Labor Statistics and all other surveys we conduct," she said.

The Post story, citing anonymous sources, said the Census Bureau had caught an employee faking data for the survey in 2010, and the practice went beyond one employee and had continued.

It said the employees had faked interviews to meet monthly quotas for the survey.

Vidal said the bureau always cross-checked and verified data collected by employees to ensure its validity.

"That monitoring process includes re-interviewing respondents, and rechecking the data an employee has submitted, looking for red flags that indicate possible fabrication," Vidal said.

The monthly employment report was watched closely in the months ahead of the election, as Obama worked to prove his leadership was turning around the economy.