Family and Medical Leave Act (FMLA) still has a "motivating factors" test and not a "but for" test.
If you are off on FMLA leave your employer cannot retaliate against for taking or requesting FMLA. While many types of retaliation require you to prove that "but for" you taking certain action (ex: requesting not to be sexually harassed) you would not have been fired or disciplined. Recently a Federal District Judge was asked if the "but for" test should be used in FMLA cases.
The "but for" test and the "motivating factors" test may seem trivial to employment lawyers but the stakes are high for employees as to which test applies. If your firing is simply a motiving factor (but not the only factor) in your termination you can win a case. But, if you are required to prove that your firing would not have happened "but for" your request for FMLA it makes it much easier for a Judge (probably not a jury) to dismiss your case. The "but for" standard allows employers to simply come up with any other reason and say that your FMLA claim might have been a motiving factor for your termination however it was not "but for" your FMLA claim that you were fired. Fortunantly this particular district court judge below ruled that the standard is "motivating factor", but this case will almost certainly be appealed to the 5th Cir, (which jumps through hoops to hurt employees and help employers) and I suspect they will make the standard "but for". It will probably take the US Supreme Court to settle the matter, but with recent appointments of anti-employee judges by President trump there is not a lot of hope.
Garcia v. Randolph-Brooks Fed. Credit Union (2020) the trial judge noted that in Richardson v.
Monitronics Int'l, Inc., 434 F.3d 327 (5th Cir. 2005), the Fifth Circuit applied the “mixed motive” rule of
causation to an FMLA retaliation claim, placing the burden of disproving causation on the employer after the
plaintiff proved that retaliatory intent was a motivating factor even if it was not the only factor. However, after the decision in Richardsons, the U.S. Supreme Court rejected the “motivating factor” rule and adopted a “but for” approach in
interpreting some other employment laws (not the FMLA). The employer argued that the district
court should apply a “but for” rule in an FMLA retaliation case in view of U.S. Supreme Court’s interpretation
of other laws. The trial court noted that the Fifth Circuit has not yet reconsidered its decision in Richardson and therefore applied the “motivating factor” rule and not the "but for" rule. A
supervisor’s criticisms of plaintiff’s repeated FMLA created an issue of fact whether the plaintiff’s FMLA
leave was a motivating factor in the employer’s decision to terminate the plaintiff’s employment, even if other
factors contributed to the employer’s decision. The employer bore the burden of proving that it was the other
factors, not retaliatory intent, that caused the plaintiff’s discharge.