When the Communications Workers of America (CWA) leveled allegations of union-busting at T-Mobile USA last week , it wasn’t anything new: The union has been criticizing the carrier since it entered the U.S. market in 2001.

T-Mobile USA may be the focus of CWA’s current union-advocacy efforts but that’s not to say the labor organization doesn’t have equally harsh words for the rest of the wireless space. The CWA has taken a hard line on what it claims are anti-union activities from all the leading U.S. operators except AT&T, which is the only union shop among the top four carriers.

“You could put T-Mobile, Verizon Wireless and Sprint in the same category when it comes to unions,” says CWA rep Candice Johnson.

CWA claims that T-Mobile, Verizon Wireless and Sprint all engage in systematic anti-union activities ranging from intimidation to closing call centers where workers are trying to organize.

Not surprisingly, the carriers either roundly deny these claims or decline to comment. It’s illegal for them to be openly anti-union and admitting anything other than a neutral stance on labor organizations will land them in hot water with the National Labor Relations Board (NLRB).

Verizon Wireless didn’t respond to requests for comment about the CWA’s complaints but Sprint said it was proud that its employees were non-union, though it supports the right of employees to choose third-party representation.

“Because we treat our employees with fairness and respect, we can talk to each other, work together and have a positive environment. Our employees have chosen not to be represented by any labor union, and we are proud of that,” the company said in a statement. “There are many ways employees can bring problems to management’s attention and get them resolved without having to go outside the organization or fearing retaliation.”

CWA says otherwise, but it’s difficult to prove whether the group’s allegations are true. Much of what the organization alleges is based on anonymous accounts by current and former workers who are extremely reluctant to testify about their employers. Complaints filed with the NLRB provide additional anecdotal evidence, but many of the complaints never reach an official reprimand from the agency.

A few items that do seem to support CWA’s claims can be found by doing a search of the NLRB’s electronic records. The records show that Verizon Wireless was found in violation of National Labor Relations Act in 2007 when the NLRB ruled it had illegally banned union solicitation of employees.

NLRB’s records also show Sprint was in violation of federal labor laws when it closed a financially troubled call center after employees there attempted to unionize. CWA frequently cites the case as an example of Sprint’s supposedly anti-union activity, but the case dates back to 1996, making it an inaccurate comparison to current attitudes and actions of Sprint management.

T-Mobile has never faced a formal ruling from the NLRB but aspokeswoman from the agency said there were “a number of union charges againstT-Mobile” filed with the NLRB. All the charges were either dismissed orsettled, allowing T-Mobile to avoid an official reprimand.

T-Mobile has taken the brunt of CWA’s most recent complaints. CWA alleges that T-Mobile parent Deutsche Telekom (DT) has a double standard for its unionized German workforce and nonunion U.S. workforce. The group has teamed up with ver.di, the union which represents DT’s German workers, to put international pressure on the company.

Specifically, CWA claims that Deutsche Telekom’s employees in Germany make more money than U.S.employees. CWA based its allegations on a Deutsche Telekom human resources report which compared the personnel costs of its 131,000 German workers to those of its 57,00 international employees.

 CWA claims that the report confirms that DT’s union employees in Germany make more than their U.S. brethren. That’s not entirely accurate.

 All the report really proves is that German employees cost Deutsche Telekom more that its international employees, a fact the company attributes to the fact that it has a large civil servant population in Germany “which tends to be more cost intensive.” DT’s headquarters and its work-intensive fixed line network are also included into its German personnel costs, pushing the figure even higher.

CWA also claims that DT’s union employees in Germany work a 38-hour week whereas its U.S. employeeswork a full 40 hours per week. This, too, is not entirely true.

The 38-hour work week only applies to 6,000 employees at a German technology center who negotiated a special deal through union representatives.

Finally, CWA alleges that T-Mobile engages in anti-unionactivities like intimidating workers who try to organize.

T-Mobile USA characterizes the allegations as “fallacious”and “misleading rhetoric,” saying it complies with U.S. law requiring it to be neutral when it comes to union organizing.

“T-Mobile USA respects the rights of unions to exist and recognizes and respects employees’ rights to organize or to refrain from organizing. To date, T-Mobile employees have chosen not to join any union,” the company said in an April 9 statement.

Lowell Turner, a professor of international and comparative labor at Cornell University, says that unionization in the telecommunications space can be traced back towhen AT&T still had a monopoly hold on the U.S. phone market.

“When AT&T was broken up into the baby bells, companiesstarted to open up into new technologies,” he says. “When those companiesopened up new units, they were kept non-union.”

AT&T Mobility is the only top wireless provider in the United States tohave a union workforce. Though Verizon’s landline employees are unionized withCWA, the carrier has just a smattering of union wireless employees. Union representation at Sprint ended with the 2006 spin-off of its landline unit, Embarq. T-Mobile USA has no union representation.

Turner says the fact that AT&T Mobility is the only top operator in the nation to still have union representation is a carry over from its legacy wireline unions. “AT&T said they’d stand back and be neutral [on unions],” he says. “Once management really is neutral workers almost always decide they want to go with a union. The trouble at the other operators is that they were never genuinely neutral.”

Depending on whom you believe, companies are either conspiring to keep their workers from organizing or are completely neutral. The truth probably lies somewhere in between, but the mishmash of anecdotal evidence and incomplete data on the issue makes it difficult to draw a clear line.