How on earth does Tebow have any standing to complain? Sure, anyone can send a cease and desist letter to anyone for anything, but generally you don't unless you have at least some basis in law to entertain a lawsuit.
The comments section for this article is awesome. For example "the real question is, could the actual jesus send the jets to the super bowl. hard to say."
Copy-cat Jesus shirts are a big industry, with look-a-like logos. As a graphic designer, it's fun to see , like Christian Wacky Packages ('member those?)
Tebow seems to be making a big fuss over nothing. The tops aren't bad, they're not taking the mickey and they look nice. They also have a good religious theme. It doesn't seem like there's much cause for complaint.
From what I can see, the complaint is probably the wording on their website which does mention Tebow.
As they merely talk about Tebow coming to NY and his religious beliefs, and how New Yorkers will likely have faith in Tebow to work miracles with the Jets, I doubt the claim will be seen to have merit. In this case, I see no implication that Tebow is endorsing the t-shirt and, as a public figure, they have a right to talk about the news Tebow has generated.
I do agree, however, the complaint will likely generate plenty of sales of this shirt.