It must have been late on Friday when the ANZ advised the ASX that it would be undertaking a global roadshow this week in relation to a potential US dollar denominated Additional Tier 1 capital issue, because the news only broke yesterday. If ANZ does raise AT1 capital from international investors, it will be the first of the Big Four banks to do so.  In fact, our major banks have not even attempted to issue AT1 capital to domestic institutional investors in the wholesale corporate bond market. Issuance to date has been limited to retail investors via the ASX. Retail investors have demonstrated considerable appetite for high yielding securities that come with franking credits, although this appetite has waned since the oversupply of such product in 2014.Last year was a miserable one for AT1 issuers and investors alike, with margins on the securities moving steadily wider. The trend was only broken with CBA's PERLS VIII securities sold in March with a margin of 520 basis points, the widest yet seen in the market.While other AT1 issues could be bought in the secondary market offering superior yields to maturity, the highest available running yield attracted many investors. Since then, margins and yields have been contracting. So much so that Westpac set the margin on its upcoming Capital Notes 4 AT1 issue at 490 bps and has raised A$1.45 billion so far. And this may bring us to the nub of the problem confronting ANZ.ANZ has A$2.0 billion of AT1 securities due to be called in December, as well as any need it may have to raise new AT1 capital. This will be a large amount for the market to absorb, with CBA's PERLs VIII having already raised A$1.45 billion, Westpac's Capital Notes 4 issue will almost inevitably be even larger, NAB has flagged its interest in issuing AT1 capital this year and CBA has said it might even come back with another issue.If all of this supply does come to market, then margins will blow out once again, and repeat of 2014/15 could be looming. The fact is that each of the major banks need to find an alternative market for their AT1 capital issues.Domestic institutional investors have shown very little interest, with there being only marginal participation in the issues listed on the ASX. So ANZ is looking offshore.The international market for CoCos, as the AT1 instruments are known (short for 'contingent convertibles'), has bounced back strongly over the last month or so after having been savagely sold off in the first quarter, when it was feared that Deutsche Bank would miss a coupon payment. In early February, the value of the six per cent CoCo concerned fell to 71 cents in the euro.But that was long ago, and the market is hot once more. Obviously, this is what ANZ wants to take advantage of but will the economics work?Coupon, or rather dividend, payments on AT1 securities come with franking credits and are therefore not tax deductible. Any market ANZ issues