The IRS' Employee Union Historically Gives 90%+ to Democrats

The IRS is accused of targeting Tea Party and similar groups for excess scrutiny when these groups applied for tax-free 501(c)(4) status.  Various reasons for the extra scrutiny is alleged.  However, does the IRS' own public-sector employee union play a role?

IRS employees are organized by the National Treasury Employees Union (NTEU), who also manages employees within other divisions of the federal government.  The Tea Party groups advocate for smaller, more affordable government which is in direct conflict with employees and their union within the federal government.  Is this the reason for the additional IRS scrutiny?

While the NTEU isn't among the bigger political spenders at the national level, historically, they give roughly 90% or more to Democrats.