Perhaps these articles may be useful:

Cyclicality of Wages and Union Power - http://doku.iab.de/veranstaltungen/2011/ws_ees2011_annaig_paper.pdf

Wage Rigidity, Collective Bargaining, and the Minimum Wage: Evidence from French Agreement Data - http://www.banque-france.fr/fondation/gb/telechar/pdf/2010/AvouFouGau_060510.pdf

Unions Power, Collective Bargaining and Optimal Monetary Policy - http://www.wiwi.uni-frankfurt.de/profs/faia/welcome_files/Unions_EI_2ndrevision.pdf

You can look at the paper by David Card & Sara de la Rica, 2006. "Firm-level contracting and the structure of wages in Spain," Industrial and Labor Relations Review, ILR Review, Cornell University, ILR School, vol. 59(4), pages 573-592, July.

A review of the literature is

Bryson, Alex (2007) The effect of trade unions on wages Reflets et Perspectives de la Vie Economique, 46 (2/3). 33-45. ISSN 0034-2971

Hope this helps.

SM

Thank you! It will be very helpful.

I have recently finished my PhD about this topic. I can recomend you to read the classical papers of FREEMAN AND MEDOFF (1979), "The two faces of unionism" and "What Do Unions Do?" (1984).

Also, Card y de La Rica, as anyone recommended before, and other papers very important:

- BLANCHFLOWER, D. y BRYSON, A. (2004): “What Effect Do Unions Have on Wages Now and Would Freeman and Medoff Be Surprised?”

- CALMFORS (1985), “Trade unions, wage formation and macroeconomic stability- an introduction"

- DAVIS, S. J. y HALTINWANGER, J. (1991): “Wage Dispersion between and within US Manufacturing Plants, 1963-86”

- FREEMAN, R. B. (1980): “Unionism and the Dispersion of Wages”

Hope this could help you! :)

I would also recommend this classic book on the impact of trade unions on wages and employment:

Booth, Alison (1994), The Economics of the Trade Union, Oxford University Press

See also Farber, Henry S. "The Analysis of Union Behavior," from the Handbook of Labor Economics, Vol. II, Chapter 18, ed. by Ashenfelter and Layard, North Holland Publishing Co., 1986, pp. 1039-1089.