The phrase “yea or nay” has a long and storied history, dating back at least to the Middle English. It was used in archaic voting contexts. A person would ask a jury, electorate or other group of people if they wished to do a certain thing or not, then follow with the phrase “Yea or nay?” It meant that they wished the people to answer yes or no, and this meaning has survived to the modern day.
Although the colloquial speech of the Internet is dynamic and ever-changing, the terms which we use to express ourselves have long histories outside of the World Wide Web. It is acceptable, in common Internet conversation, to write the phrase “yea or nay” as “yay or nay.” It may even be, according to context, broadly amusing. It is, however, incorrect, and it is not appropriate for creative writing, serious conversation or educational contexts.
The word “yay” also has a specific meaning. The two words “yay” and “yea” are pronounced exactly the same and cannot be distinguished from each other in spoken speech. However, “yay” is considered to be more of an excited interjection, and it is more often heard aloud. “Yea” is almost never encountered outside of this particular phrase. This is one of the reasons why spelling is so important on this issue. Any educated reader who is aware of the existence of the phrase will immediately recognize that “yay” is a misspelling, and it will give them the impression that the writer is not well versed in grammar and spelling.