29 C.F.R. § 102.6
Pertinent and significant authorities that come to a party's attention after the party's submission to the Administrative Law Judge or the Board has been filed may be brought to the Judge's or the Board's attention by the party promptly filing a letter with the judge or the Board and simultaneously serving all other parties. The body of the letter may not exceed 350 words. A party may file and serve on all other parties a response that is similarly limited. In unfair labor practice cases, the response must be filed no later than 14 days after service of the letter. In representation cases, the response must be filed no later than 7 days after service of the letter. No extension of time will be granted to file the response.
29 C.F.R. §102.6