VANCOUVER, March 1 (Reuters) - Canadian retailer Mountain Equipment Co-op (MEC) said on Thursday it suspended new orders from five outdoor activity brands owned by Vista Outdoor Inc , which also makes guns and ammunition, as the U.S. gun control debate spilled across the border.

The Vancouver-based adventure retailer does not sell guns but rather products like water bottles and helmets made by Vista-owned brands such as CamelBak and Bollé. Utah-based Vista also owns Savage Arms, which makes assault rifles.

"It has recently come to light that several brands MEC sells are owned by a corporation that has holdings in the manufacture of assault-style weapons," MEC Chief Executive David Labistour wrote in an open letter to customers on Thursday.

"Thousands of MEC members have contacted us to express their concerns and to ask that we stop selling products made by these brands," he added, noting the company had also heard from people who felt MEC should not get involved in the gun control debate.

Labistour said that after careful consideration, the company determined it would stop ordering new products from Vista-owned brands effective immediately, although existing inventory will stay on the shelves until it sells out.

More than 50,000 people signed an online petition urging MEC to cut ties with Vista. A similar petition from customers of Washington state-based Recreational Equipment Inc (REI) has about 15,000 signatures.

A number of U.S. companies have changed their gun-sale policies after a gunman armed with a semi-automatic AR-15-style assault rifle killed 17 people at a Florida high school last month. The mass shooting ignited a wave of student activism across the United States to press for firearms restrictions.

Retailers like Kroger Co and Walmart Inc have said they will stop selling firearms and ammunition to buyers under the age of 21, while transportation companies like Delta Air Lines Inc and Hertz Global Holdings Inc have severed ties with the National Rifle Association gun rights group.

(Reporting by Julie Gordon in Vancouver; Editing by Peter Cooney)