A bill working its way through Congress that changes how employees can create and join unions is facing tough criticism from workers who say it gives unions the green light to use aggressive tactics to get them to sign up.

The Employee Free Choice Act -- known in Congress as the "card check" bill -- calls for an easier system to allow employees to form, join, or assist labor organizations. Under the bill, employees can request blank cards from existing unions that employees can sign to express interest in joining the union. If 30 percent of employees sign the cards, companies can hold secret-ballot elections to decide on unionization.

But workers at the Dana Corporation Auto Parts plant in Albion, Ind., say the card check process has nearly torn the 50-person plant apart after harassment and intimidation from the United Auto Workers union forced them to a secret-ballot vote.

A union organizer came to the plant two years ago to ask employees to join the UAW because the company had signed a neutrality agreement with the union.

The meeting, however, did not go well, according to plant employee Larry Guest.

"He was using real rough language -- cursing. It didn't go over well with the women at all. There were a couple that just got up and left," Guest told FOX News.

Employees said union representatives approached them in the break room, at the plant doors and even followed them to their cars.

"He was just like an itch that you couldn't scratch. He just wouldn't go away," said employee Rita Murphy.

"After a while we realized he was going to be here morning, noon and night until he got his numbers that he needed," said Betty Pop.

Dana employee Jamie Oliver told FOX News that she was approached at her home.

"We're here in a little town and we're a plant of 50 some people -- you know the last thing you need is to have the union coming to your door saying I want your name," Oliver said.

The union's relentless approach, she said, eventually wore her down.

"When they approach you every day -- every day, every day," she said, "after a while it's like 'Okay. Fine. I'll sign the card.'"

The UAW collected the necessary signatures, but plant employees appealed to the National Labor Relations Board that ruled the employees could hold a secret election.

"When they held the election, there was no more union," said Guest. "Although it was close."

Now, employees say, the forced choice has turned friend into foe, causing some employees to be threatened by coworkers who had wanted the union.

One employee said she was threatened for her choice.

"I have my reasons for the way that I voted. That's nobody else's business, and had it not been for the card check, nobody would know if I was for or against," said Beverly Musolf.

The UAW declined to give comment to FOX News on the employees' complaints.

The latest version of the Employee Free Choice Act was introduced to both chambers of Congress on March 10, 2009.

FOX News' Brian Wilson contributed to this report.