Can not renew TN once sub-mit 140

Refer to Zhang & associates' website.
http://www.hooyou.com/tn/tn.html
...
To maximize the chances that their legal status to work in the US is not affected when they initiate their immigration process, we suggest TN holders do two things. First, TN holders should try to renew their visa immediately before they submit their I-140 to prolong their TN status. Usually it is permitted to renew a visa up to 6 months before its expiration. Second, we suggest TN holders apply for H-1B as a backup when the H-1B quota becomes available in April, 2008. H-1b visa/status allow the beneficiary alien to have dual intents and immigrant petition will not impact application or renewal of H-1B visa/status.