A spokesperson for the O'Rourke campaign did not return requests for comment.
The efforts by O'Rourke's campaign to host a fundraiser in New York, almost 2,000 miles away from Texas, are the latest example of its efforts to keep up with Cruz and giving him a run for his money for a seat that has been held by a Republican since 1993.
O'Rourke's growing popularity has led to a behemoth grassroots fundraising operation. He has brought in $9 million in small contributions, accounting for just more than 41 percent of his total. He has raked in $13 million in donations over $200, as well.
O'Rourke has also had a strong presence on social media. His speech defending the rights of players in the National Football League to take a knee during the national anthem went viral.
Going into the final three months of the election, Cruz and O'Rourke are nearly even in their total fundraising haul with the Republican senator raising $23.33 million through July and the congressman bringing in $23.36 million during the same time period, according to the Center for Responsive Politics
O'Rourke has also had a surprise showing in the polls. A Real Clear Politics polling average shows O'Rourke trailing Cruz by just more than 3 points.
With the two Texas lawmakers dead even in campaign financing and separated by only a few points in some surveys, Republican strategists have been sounding the alarm bells to outside spending groups that it might be high time for them to get involved in the election.
The nonprofit conservative group Club for Growth barnstormed Texas, as its president, David McIntosh, recently completing a fundraising swing through the state. The group also unleashed a major advertising buy, which is part of its seven-figure television campaign to back Cruz.
The Senate Leadership Fund, a super PAC linked to former aides of Republican Senate Majority Leader Mitch McConnell, has also not ruled out wading into the race. The PAC has no immediate spending plans for Texas, according to a source with direct knowledge of the matter. A spokesman for the group declined to comment.
McConnell himself admitted on Tuesday that Cruz faces a tough fight in the traditionally deep red state, but he still expects the incumbent lawmaker to pull off a victory.
"I think Ted's got a competitive race by all indications," McConnell said at a news conference in Kentucky. "We certainly expect to win Texas, but I think he does have a competitive race."