A common corporate structure that has allowed dozens of Chinese companies to get listed on U.S. exchanges is drawing increased scrutiny from American audit regulators. Chinese Internet companies such as Sina Corp. and Baidu Inc. have used so-called variable interest entities, or VIEs, to work around Chinese restrictions and seek foreign investors since 2000. Now, the Securities and Exchange Commission is also asking questions about the structure, said Paul Boltz, a Hong Kong-based partner at Ropes & Gray LLP, who cited comment letters the agency sent to six companies since December. Judith Burns, an SEC spokeswoman, declined to comment.