Canada's envoy to the United States says he is embarrassed it is taking so long for Parliament to pass a new law that would pave the way for greater pre-clearance at the border.

Ambassador David MacNaughton says he leaned on U.S. lawmakers to pass a law that would allow passengers to be pre-cleared at a greater number of airports to allow the speedy flow of people across the 49th parallel.

But Canada's bill has been before the House of Commons public safety committee for several months.

MacNaughton told a Senate committee he regularly gets asked by Americans where the accompanying Canadian legislation is and he's embarrassed to say it is not ready.

At the moment, passengers flying to American cities through eight major Canadian airports can be pre-cleared there by U.S. Customs and Border Protection officers.

That program is to be expanded to Billy Bishop Toronto City Airport and Quebec City's Jean Lesage International Airport and in March the two countries agreed to expand it to other, unspecified locations.