It may not be illegal, but it has a few negative secondary effects, among them:
1) reduces the value of US hardware on the international market, as businesses want to use equipment without backdoors installed by foreign intelligence services
2) pits the intelligence community against large portions of the tech sector, who because of market pressure will be forced to consider such activity a security threat
3) obliderates any moral high ground from which to stand on to condemn foreign intelligence services for doing the exact same thing, e.g.the State department's hypocritical efforts to condemn the Chinese for various forms of espionage in which the NSA apparently routinely engages
1) reduces the value of US hardware on the international market, as businesses want to use equipment without backdoors installed by foreign intelligence services
2) pits the intelligence community against large portions of the tech sector, who because of market pressure will be forced to consider such activity a security threat
3) obliderates any moral high ground from which to stand on to condemn foreign intelligence services for doing the exact same thing, e.g.the State department's hypocritical efforts to condemn the Chinese for various forms of espionage in which the NSA apparently routinely engages