An increase in taxes does two things. It means there's a lower return on investment for the company and therefore the share value will fall. It also means there's less money to distribute in dividends, and unretained earnings by the company, so there's less of a dividend. Both of those have a negative impact on any investor holding the stock, and, as you say, these are some major investments that any pension plan would hold.
On November 1st, 2011. See this statement in context.