Qantas' decision to enforce the "smart casual" dress code more strictly in its main capital city lounges has led to complaints from passengers refused entry for wearing thongs - including designer leather ones that had not been on the airline's initial list of banned clothing.

Qantas in February announced that the smart casual dress guidelines for guests entering its domestic Qantas Clubs and Business Lounges in Sydney, Melbourne, Brisbane, Perth, Adelaide and Canberra would be "more closely applied" from April 1, due to complaints from some passengers that dress standards had dropped.

Smart casual: Qantas is enforcing a smarter dress code in its lounges.

"Singlets, bare feet, rubber thongs and clothing with offensive images or slogans are, in most cases, likely to be deemed unacceptable," Qantas said.

"Eligible lounge visitors wearing uniforms will still be permitted to access our lounges, and this includes hi-vis work wear."