Zatlers, who besides Latvian also speaks fluent Russian and English, earlier said on national radio that he would not use the Russian language with foreign journalists and that the decision would not disappoint Russian-speaking residents of Latvia.
"Latvia has only one state language and it is Latvian," he said.
Juris Sokolovskis, a co-chairman of Latvian opposition party For Human Rights in a United Latvia, has criticized the president's decision, saying that Zatlers risks pushing away the Russian-speaking population.
Zatlers signed this week amendments to the Administrative Violations Code, previously approved by parliament, which raised fines for the use of nonofficial languages by employers and employees, and expanded the scope of the sanctions.
The move irritated Moscow with Russia's Foreign Ministry accusing Latvia of violating the rights of ethnic minorities.
"It is obvious that such discriminatory moves violate the rights of ethnic minorities, which are generally acknowledged in present-day Europe, and aim to further displace the native-Russian speaking one-third of the Latvian population from all fields of public and business activity," a spokesman for the Russian ministry said on Saturday.
Latvia, where native Russian speakers account for at least 30% of the population, treats Russian as a foreign language. Most of other former Soviet states, while maintaining only one state language, have given Russian varying degrees of recognition.