R. Alison Felix (Federal Reserve Bank of Kansas City) & James R. Hines, Jr. (Michigan) have posted Corporate Taxes and Union Wages in the United States on NBER.  Here is the abstract:

This paper evaluates the effect of U.S. state corporate income taxes on union wages. American workers who belong to unions are paid more than their non-union counterparts, and this difference is greater in low-tax locations, reflecting that unions and employers share tax savings associated with low tax rates. In 2000 the difference between average union and non-union hourly wages was $1.88 greater in states with corporate tax rates below four percent than in states with tax rates of nine percent and above. Controlling for observable worker characteristics, a one percent lower state tax rate is associated with a 0.36% higher union wage premium, suggesting that workers in a fully unionized firm capture roughly 54% of the benefits of low tax rates.

See also Wall Street Journal:  Union Workers Hit Harder By High State Taxes, Study Finds:

Union employees bear more of the burden of high state corporate taxes than non-union employees, according to a new study distributed by the National Bureau of Economic Research.

That suggests that in high-tax states like Pennsylvania and New Jersey, taxes take a bigger bite out of pay for union members than non-union workers in similar circumstances. Conversely, union workers may have more to gain from low taxes in places like Texas or Wyoming than non-union employees.