He implied that the foreign carrier could exert control beyond its voting stake in the airline and beyond its seat on the board.
Salomon said that at the close of business on Tuesday, Berkshire's voting stake came to 19.9976 percent.
Air Canada's voting stake will now fall to 4 percent.
Investors holding more than 50% of voting rights would be forced to lower their voting stakes within a year.
It is unlikely that the Roberts family would agree to dilute its voting stake.
That constituted about 78 percent, or a voting stake of about 72 percent in the company.
Liberty Media now has the second-largest voting stake after the Murdoch family interests.
The tactic is a complex hedging technique that allows an investor to buy a voting stake without actually holding an economic interest in the company.
Simon Property has taken the company to court, challenging the way the family obtained its voting stake in Taubman Centers.
As a result of that transaction, the family's voting stake of 29.8 percent will be reduced slightly, to 29.45 percent.