The campaign of New York Governor Andrew Cuomo is challenging the Democratic Party primary petition of Zephyr Teachout, a law professor who is also seeking the Democratic nomination for Governor. See this story. She submitted 45,000 signatures and needs 15,000 signatures of registered Democrats. Apparently Cuomo is not challenging the Democratic primary petition of Randy Credico, the third Democrat who filed. Thanks to Rick Hasen for the link.
Three times the requirement? The validity rate would have to be ridiculously low for the challenge to succeed.