ABC News' Sandra Lee reports:

In the uncertain world of online dating, finding your true love is like finding a needle in a haystack. And now one site is adding another twist to the never-ending checklist for potential suitors.

The popular dating website OkCupid.com is raising eyebrows by offering a filter to sort by body type, leaving some users outraged.

"I think to discriminate really against somebody based on physical aspect that can be changed is completely unfair," Donna Barnes, author of "Giving Up Junk-Food Relationships," told ABC News.

For an extra fee of $5 to $10, users can weed out various shapes and sizes of their potential dates, which is something the co-founder of OkCupid, Sam Yagan, defends as a true-to-life dating option.

"If you were at a bar deciding who you wanted to talk to, of course physical appearance is something you take into account," explained Yagan.

But OkCupid members, like Alana Massey, 28, says the feature can make online dating even more stressful.

"How you self-identify on the site, and how you're going to be perceived on your date by your date, is going to be a point of potential insecurity," said Massey.

But Yagan argues that the option of choosing a body type is just that-an option.

"The idea that it is somehow pejorative I think just doesn't hold water, just by the fact that people are choosing to self-identify that way," he said. "I think it is an obvious feature of a dating site."

"You always have an option not to fill in anything you're not comfortable with revealing about yourself online," added Barnes.

And online dater, Massey, says despite the controversy she's staying on the site, still hoping to find Mr. Right.

"I think that everyone who uses the site and uses the feature understands they like what they like," she said."I've gone on great dates. [I] have a few people in the pipeline, so we'll see how it ends up."

The CEO acknowledges this is a very sensitive issue for many people, and reiterates that the option to choose body type or attractiveness is reserved for premium service users.