Amid growing concerns about possible violence and vote fraud on Election Day, the Oath Keepers, a national group of former military and law enforcement officers, has urged its members to “blend in” with voters and do “incognito intelligence gathering and crime spotting” at polling places across the country on Nov. 8.

“In particular, we are calling on our retired police officers, our military intelligence veterans, and our Special Warfare veterans (who are well trained in covert observation and intelligence gathering) to take the lead,” group leader Stewart Rhodes said in a “call to action” on the group’s website and in a YouTube video urging members to “help stop voter fraud.”

The Oath Keepers are officially nonpartisan, but their concerns clearly echo Republican presidential nominee Donald Trump’s warnings about a “rigged” election and his calls for his supporters to monitor polling places for evidence of fraud by supporters of Democratic rival Hillary Clinton.

Noting recent undercover video shot by conservative activists, Rhodes, a Montana attorney and Army veteran, told his supporters he is worried about “criminal vote fraud on an industrial scale.”