The former MPs face a five-year ban from politics if the National Legislative Assembly (NLA) votes in favour of impeachment on 14 August, threatening to remove more key allies of the Shinawatra clan whose parties have swept every election since 2001.
The ex-lawmakers are accused of supporting an amendment to the country's charter aimed at making the upper house a fully elected chamber that was later deemed unconstitutional.
If impeached they would follow in the footsteps of Yingluck, who fell foul of the NLA in January over a separate issue.
"The assembly has finished hearing the case against the former MPs" and will vote next Friday, NLA speaker Jetn Siritharanont told AFP.
A successful impeachment requires 132 out of 220 assembly members to vote in favour, he added.