Example of Employee Discrimination?

Mike is a 27 year veteran employee, who currently holds a very coveted position in a factory that keeps him away from the riskier areas of his workplace. In the 3 years Mike has held this coveted position--he's done impressively well and fully meets job expectations.

Lisa is about to make her first year in the same factory, but works in a area that carries certain inherent employee risks.

Lisa is a few weeks pregnant--and the workplace bosses--along with Lisa's co-working husband--are fast concerned for her safety; "temporary" job reassignment is inevitable.

Mike's immediate supervisor informs him of Lisa's situation that MIGHT have him pressed to step down from his coveted position--and work the lesser attractive position Lisa works in. Do note: There are 2 other reassignment possibilities--work areas currently held by FEMALES, but for evident reasons, Mike's position is likely targeted.

If Mike is made to work Lisa's work post, is he being discriminated against? Does Mike have any legal ground to protect his position from being taken over by Lisa?