According to the Associated Press, which obtained a copy of the memo from independent newsletter Mine Safety and Health News, the United Mine Workers of America said the document is a standard tactic for companies attempting to discourage unions.

"Signing a union authorization card is like signing a blank check. You will not know what it is going to cost you or your family in the future," the AP reported of the memo’s contents, adding that it reminds individuals that they have a legal right to not sign any documents.

"Unions are a business … [they] need monthly dues and assessments from employees to survive," the letter reportedly said.

"We believe you need to keep all of your take home pay and not share it with any union."

Alpha told the news service that it is indeed a standard practice, but one for communication to staff regarding their rights.

"It's not uncommon for the mine management to post these policies so as to inform people of the rights they're entitled to under labor laws," Alpha spokesman Ted Pile said.

UMWA spokesperson Phil Smith responded that the language of the memo is “straight out of a union-busting consultant's playbook".

"I suspect that something similar is posted at just about every one of the larger non-union mines in America, no matter who owns it," he said.

Safety and work practices have been under the microscope at UBB for some time; investigators have cited both factors as the cause of an April 2010 explosion at the West Virginia mine that killed 29 workers.

During a recent briefing on its probe of the accident, the US Mine Safety and Health Administration pointed to methane and coal dust as triggers for the blast.

MSHA also revealed two sets of safety records being kept at the mine, one for inspector review and another set for its production staff that provided a more accurate picture of conditions.

The agency is still working on its final report and said it will probably be October before it is released.

UBB was a non-union mine at the time of the explosion, though the UMWA is representing some of the miners in the investigation.

Smith told the AP he was not aware of any active organizing campaign at the operation.

The union currently represents about 1500 Alpha employees and thousands of retirees after signing the newly-ratified 2011 National Bituminous Coal Wage Agreement earlier this month.

The collective bargaining agreement covers two large Pennsylvanian coal mines and Alpha’s Cumberland and Emerald complexes in Green County.

The BCOA deal was ratified by union members late last month, locking in the UMWA’s largest ever pay increase structure for the next 5.5 years.

Union members nationwide voted with a 70% approval rate for the deal, set to extend from July 1, 2011 to December 31, 2016.

It includes a wage increase of $US6 per hour over the life of the agreement; two $1-per-hour increases will go into effect in the first six months of the agreement on July 1, 2011 and January 1, 2012.

Those increases are 8.2% higher than current wages.

Pay will then rise by $1 per hour on January 1 of each of the deal’s successive years.