Shares of the Global X FTSE Greece 20 ETF (NYSEArca: GREK) are down 4.6% Thursday on news the country will not make a tax on foreign owners of Greek debt retroactive.

Yields on Greek 10-year sovereign bonds surged 8% to highest levels in almost two months, according to Bloomberg data.

Soaring Greek yields adversely affected bond yields in fellow PIIGS countries Italy, Portugal and Spain, sending the iShares MSCI Italy Capped ETF (NYSEArca: EWI) down more than 3% and the iShares MSCI Spain Capped ETF (NYSEArca: EWP) lower by 2.3%.

“But capital-gains tax still applies to foreign holders under a regime in place from Feb. 29, 2012 to Dec. 31, 2013. That tax rate is 33% for legal entities and 20% for individuals. Companies and individuals domiciled abroad holding Greek bonds bought during that period could still be exempt from the old tax, if the country they are based at has a double-tax agreement with Greece,” reports Matina Stevis for the Wall Street Journal.

GREK’s tumble comes on an already bleak day for emerging markets ETFs, but with a heavy volume loss of just under 5%, GREK is one of the day’s worst-performing single-country ETFs tracking developing world equities. Three major index providers, including MSCI, demoted Greece to emerging markets status last year. [Greece Gets Emerging Markets Demtion]

GREK has recently been struggling compared to the other PIIGS country-specific ETFs. Over the past 90 days, the lone Greece ETF is down 8% while EWP and EWI are up an average of 6.6% over that time. [Investors Pour Into PIIGS ETFs]