What is the test for an employee to bring a claim for unlawful retaliation against their employer for their speech?

To state a claim for unlawful retaliation in violation of the First Amendment, an employee must first demonstrate that the speech was "on a matter of public concern." Connick, 461 U.S. at 145. Unless the speech meets this threshold requirement, we need not balance the employee's speech interest against the employer's interest in efficiency, see Pickering v. Bd. of Educ., 391 U.S. 563, 568, 20 L. Ed. 2d 811, 88 S. Ct. 1731 (1968), nor need we evaluate the causal relationship between the speech and the adverse employment action, see Mt. Healthy City Sch. Dist. Bd. of Educ. v. Doyle, 429 U.S. 274, 285-87, 50 L. Ed. 2d 471, 97 S. Ct. 568 (1977).