Regarding the first part of your question, we were not able to find the figure you were seeking. We did find some good leads, however, in this article:

AUTHOR: Beverly P. Lynch
TITLE: Public Library Service to Business
SOURCE: Public Libraries v37 no6 p382-6 N/D ’98

"PUBLIC LIBRARY DATA SERVICE: BUSINESS SERVICES SURVEY
In 1996 a special "Business Services Survey" was included for the first time in the 1996 Statistical Report prepared by the Public Library Association as part of its annual Public Library Data Service questionnaire.(FN7) Four of the nine questions in this survey related to the library's formal relationships with the local business community. These emphasized membership in the local Chamber of Commerce, formal partnerships with economic development groups in the area and community business, and library memberships for local business. Two questions dealt with the library's collection in business subjects and in business materials, and three related to special services to business, for example: "Does your library offer staff who are specialists in services to business?" A specific question was asked about library fees for information retrieval and research services for business topics, e.g., customized searching, data compilation: 'Does your library charge a fee for this service?'
"Eight hundred and twenty-three public libraries in the U.S. and Canada responded to this survey, with the participation skewed heavily toward the largest libraries. (The American Library Directory for 1996-97 reports 9, 165 public libraries in the U. S., excluding branches. Most of these are located in small communities.) Table 1 shows the number of libraries responding to the survey by population size.
"Not all libraries responding to the survey replied to the questions on services to business, so totals for specific questions do not add up to 823."

A page about the PLDS Questionnaire from the PLA can be found here: http://www.ala.org/ala/pla/plapubs/pldsstatreport/pldsstatistical.htm

The Kansas City Public Library has up to 1997 of the PLDS; however, the 2005 is the one you will want. You might submit another question requesting someone to look it up for you. According to WorldCat, there are only 280 or so libraries in the US that own it, and not all of them have 2005.

Also, see these other articles:

Author(s): Nelson, Patricia.
Title: Libraries Are Players in Economic Development.
Source: PNLA Quarterly v. 68 no1 (Fall 2003) p. 19-20

Title: Public libraries in the United States: service to business and industry (presented at the 1997 Kanazawa Institute of Technology International Roundtable).
Author(s): Lynch, Beverly P., 1935-
Description: p. 304-15 bibl.
In: Development of digital libraries Greenwood Press, 2001 ISBN: 0313314780

Author(s): Holt, Glen E.
Title: Changing demand for library business services.
Source: The Bottom Line v. 14 no1 (2001) p. 29-31 Journal Code: Bottom Line
Standard No: ISSN: 0888-045X

Author(s): Lynch, Beverly P., 1935-
Title: Public library service to business.
Source: Public Libraries v. 37 no6 (Nov./Dec. '98) p. 382-6 Journal Code: Public Libr
Standard No: ISSN: 0163-5506

The second part of the question, about the percentage of public libraries in the US that have space set aside for worker education about unionizing, I believe a figure is so unlikely that I did not even undertake to try even one search. I have an estimate, however: 0%.

Hope this helps.