SAN FRANCISCO, Nov 12 (Reuters) - A group of Amazon.com Inc (AMZN.O) workers in New York City"s Staten Island has withdrawn a petition to hold a union election, a spokeswoman for the U.S. National Labor Relations Board confirmed on Friday. The group, known as the Amazon Labor Union, filed its petition last month, joining an escalating push by unions to organize Amazon"s vast network of warehouse workers.It was unclear why the Amazon Labor Union withdrew its petition. Chris Smalls, a leader of the group and a former employee at the Staten Island warehouse, did not immediately respond to a request for comment. "Our focus remains on listening directly to our employees and continuously improving on their behalf,” Kelly Nantel, an Amazon spokeswoman, said in a statement.Amazon raised doubts last month about whether the Amazon Labor Union had gathered enough legitimate signatures to hold a union election. The news of Amazon Labor Union"s withdrawal of its petition was previously reported by Bloomberg. Reporting by Julia Love and Jeffrey Dastin Edi