LONDON - British Prime Minister Theresa May has lambasted the behavior of Boeing after it complained that Canadian rival Bombardier used unfair government subsidies to sell planes at artificially low prices.

Addressing a conference in London, May said Thursday that Boeing's behavior "is not the sort of behavior we expect from a long-term partner" and that it "undermines that partnership."

The government has many dealings with Boeing, particularly in defense.

May's comment follows the preliminary decision by the U.S.'s Department of Commerce to slap an almost 220 percent tariff on Bombardier's C series aircraft, which threatens more than 4,000 jobs in Northern Ireland.

May said she was working with the Canadian government and leaders in Norther Ireland to "impress" on the U.S. government the importance of Bombardier to Northern Ireland.