Employment discrimination based on the initial or native language of a prospective employee is probably not lawful under US federal law. Requiring the English-language skills actually needed for a particular job is lawful. Doing "editing, writing, or translation" obviously requires language fluency. But unless a business can demonstrate that it is impossible for non-native speakers to achieve fluency comparable to native speakers needed for a particular position, demanding a specific native language would be demanding a particular national origin, and thus be an unlawful practice.
According to 42 U.S. Code § 2000e–2
It shall be an unlawful employment practice for an employer—
(1) to fail or refuse to hire or to discharge any individual, or otherwise to discriminate against any individual with respect to his compensation, terms, conditions, or privileges of employment, because of such individual’s race, color, religion, sex, or national origin; (emphasis added)
The US Equal Employment Opportunity Commission (EEOC) has a page on "Immigrants' Employment Rights under Federal Anti-Discrimination Laws" which says:
The law protects people against employment discrimination on the basis of their national origin. Following are some examples of employment discrimination based on national origin. ...
- Unlawful national origin discrimination may include discrimination because of a person's looks, customs, or language. ...
- Treating employees differently because they have a foreign accent is lawful only if accent materially interferes with being able to do the job. ....
According to Nolo's page on "Language and Accent Discrimination in the Workplace":
A job requirement that an employee must be fluent in English is legal if fluency is required to effectively perform the position. The Equal Employment Opportunity Commission (EEOC), the federal agency that interprets and enforces the laws prohibiting discrimination, has pointed out that the degree of fluency required varies from job to job, even within the same company. Therefore, blanket fluency requirements that apply equally to the customer service department and the warehouse workers might not be legal.
According to Workplace Fairness's page on "Language Discrimination":
Language discrimination is a subset of national origin discrimination. Language discrimination refers to the unfair treatment of an individual based solely upon the characteristics of their speech; such as, accent, size of vocabulary, and syntax. It can also involve a person's ability or inability to use one language instead of another. Because language discrimination is a form of national origin discrimination, the same body of law prohibits it.
Language discrimination is the unfair treatment of an individual solely because of their native language or other characteristics of speech, such as accent, size of vocabulary, and syntax. ... Some courts and government agencies have said that discrimination based on language is a form of national origin discrimination because primary language is closely related to the place a person comes from ...
In "What Recent Court Cases Indicate About
English-Only Rules In The Workplace" by Rosanna McCalipst (U. PA. JOURNAL OF LABOR AND EMPLOYMENT LAW, volume 4 issue 2) it is said that:
Title VII of the Civil Rights Act of 1964 provides that it is unlawful to discriminate in the terms or conditions of employment based on one's race, religion, sex or national origin. There are two ways a plaintiff can prevail.
Either the plaintiff can prove disparate treatment, meaning the employer intentionally discriminated on the basis of one of the protected grounds, or disparate impact, meaning a seemingly neutral employment practice puts an undue burden on members of a protected class. ...
The disparate impact analysis was first set out by the Supreme Court in Griggs v. Duke Power Co. 401 U.S. 424 (1971). From
that case and the decisions of various courts interpreting the holding, a burden shifting analysis has emerged. There are three steps to the analysis. First, the plaintiff must establish that the policy in question has a disparate impact on a protected class. Next the employer must defend the policy by proffering a legitimate business purpose for it. Last, the plaintiff
can still prevail if it shows there is a less discriminatory method by which the legitimate business goal can be obtained.
According to "Avoiding Claims of Citizenship and National Origin Discrimination When Interviewing, Hiring, and Onboarding Foreign Workers" by the Dickinson Wright law firm:
National origin discrimination includes, but is not limited to, discrimination due to place of birth, country of origin, ancestry, native language, and may be based on a perception that the individual looks or sounds “foreign,” or any other national origin indicator.
I should add that if an employer is using "native" simply to mean "a very high level of fluency and skill with the language" then such a requirement is not discriminatory under 42 U.S. Code § 2000e–2, and quite likely not under any US law. If the employer is using "native" to mean "a very high level of fluency and skill obtained by learning the language as a young child" then the case is less clear, and most of the precedents cited above will be of only limited significance at best. I could not find a case squarely on point where a requirement for a "native speaker" in either of these senses, or indeed in any sense, was challenged.