Congressional investigators are probing a decision by the Federal Elections Commission to drop a case against a major teachers’ union that allegedly violated federal law by forcing union members to donate to its political action committee.

Claire Waites, an eighth grade science teacher and member of the National Education Association, testified at the House Oversight and Government Reform Committee in February that she was told by union leadership that a donation to the NEA’s “Children’s Fund” PAC was “non-negotiable.”

Compulsory political contributions by workers to a union’s PAC is illegal. Waites filed a complaint with the FEC in 2009, but was told later that year that the Commission would be dropping the case due to the relatively small amount of money involved (her contribution to the Children’s Fund was $100).

Rep. Darrell Issa (R-CA), who chairs the Oversight Committee, is asking for more information on that decision.

“The Committee understands that due to limited resources, the Commission must exercise prosocutorial discretion in determining whether to proceed in a matter,” explained Issa in an April 3 letter to Caroline Hunter, who chairs the FEC. But the decision, he added, “ignores the possibility that such violations, aggregated across a large organization, can result in substantial sums.”

Issa went on to note that the Children’s Fund has spent just under $9 million supporting political candidates.

The Oversight Committee is looking for specific documents pertaining to the FEC’s legal approach to the case, and information on similar cases that the Commission may have pursued, despite comparably small sums involved.

The committee’s efforts are part of an ongoing campaign by Issa and other Republicans to protect workers’ rights against encroachments by their unions. The FEC letter was announced on Oversight’s new website, ProtectingOurWorkers.com, which claims, “forced political contributions and secret special interest spending have a corrupting effect on our democracy.”

Here is the full text of Issa’s letter:

Issa FEC Letter