A lawyer representing Palestinian government agencies sent letters this week to an American sneaker company and an international hotel chain threatening a boycott and legal action if they did not withdraw their sponsorship of the Jerusalem Marathon, which the Palestinians say violates international law.

The letters to New Balance, a footwear company based in Boston, and the InterContinental Hotel Group, which includes the Crowne Plaza hotel in Jerusalem, say that the marathon, scheduled for March 1, is a “serious breach” of international law because it runs through East Jerusalem, territory that Israel captured during the 1967 war and later annexed. The Palestinians, and much of the world, consider East Jerusalem occupied territory, but the Israelis see it as part of their capital city.

“As the marathon neither caters to the needs of Palestinian civilians nor serves any genuine military purpose, the marathon constitutes an illegal activity in occupied East Jerusalem under international humanitarian law,” read the letters, sent on behalf of the Palestinian Olympic Committee, Athletics Federation and Higher Council of Youth and Sport. Citing United Nations resolutions, the Fourth Geneva Convention and an International Court of Justice ruling, the letters warn: “If your company does not immediately withdraw sponsorship of this illegal activity, my clients will be forced to pursue this matter legally.”

The letters do not specifically mention the United Nations General Assembly vote on Nov. 29 that upgraded Palestine to a nonmember observer state, but a senior Palestinian official said the companies could be targets if Palestinians leaders decide to use the new status to pursue claims in international courts. Another possibility is action by the Arab League, whose 22 member states called for a boycott of Adidas over its sponsorship of the Jerusalem marathon last year.

The mayor of Jerusalem, Nir Barkat, has described the marathon, in its third year, as an effort to make his bitterly divided and contested city “normal.” But normalcy is a challenge in a city that both Israelis and Palestinians see as their capital, a place that Jews, Muslims and Christians worldwide all revere as holy, a sprawling 48 square miles where 500,000 Israelis and 300,000 Palestinians live mostly in separate neighborhoods. Virtually none of those Palestinians vote in municipal elections, for fear of “normalization,” and many Palestinians in recent years have refused to attend meetings or hold official events in parts of Jerusalem for the same reason.

This week, Senator Marco Rubio, Republican of Florida, made headlines during a visit here for an offhand reference to Jerusalem as Israel’s capital, which Washington generally avoids. American consular officials joke that part of their job is to make sure the mail is addressed simply to “Jerusalem,” not “Jerusalem, Israel.”

Asked about the letters to New Balance and Crowne Plaza, a spokesman for Mr. Barkat said on Friday that the Palestinians were “trying to drag the marathon into a political cause.”

“This is not politics, this is sport, this is culture,” said the spokesman, Barak Cohen. “This is a major international event in a major international city,” he added, noting that 2,000 of the more than 18,000 registered runners were from 52 countries. “Arab residents and Jewish residents are welcome to participate and celebrate together,” he added.

A spokeswoman for New Balance, whose logo is at the top of the marathon’s Web site next to the slogan, “Let’s Make Excellent Happen,” did not respond to inquiries on Friday.

A spokeswoman for the InterContinental Hotel Group said the company was unaware of the marathon sponsorship, which she said was by the Jerusalem Crowne Plaza, a franchisee. She said the hotel’s manager could not be reached for comment because of the Jewish Sabbath.