The authorities in a northeastern Chinese border city have secretly warned local firms they will be slapped with fines if they newly hire North Korean workers in violation of U.N. sanctions, amounting to 5,000 yuan ($750) per worker, sources familiar with the situation said Wednesday.The move by the city government of Dandong indicates that Beijing has quietly ramped up its pressure on Pyongyang in line with tougher sanctions in response to North Korea's weapons development, as it paves the way for U.S. President Donald Trump's planned visit to China in November.Dandong authorities have not…READ FULL ARTICLE