A union representing healthcare workers has asked the board of Boston-based Beth Israel Deaconess Medical Center to consider whether a trustee, Jay Fialkow, should have disclosed that he helped raise money for the hospital from at least one person with whom he had also done business. Fialkow, a longtime Boston lawyer, is under investigation by regulators for having introduced his clients to Richard Elkinson, a Framingham, MA, man who is facing fraud charges for having allegedly stolen $29 million from investors.